2. Common infrastructure
2.1. Terminology
This specification refers to both HTML and XML attributes and IDL attributes, often in the same context. When it is not clear which is being referred to, they are referred to as content attributes for HTML and XML attributes, and IDL attributes for those defined on IDL interfaces. Similarly, the term "properties" is used for both JavaScript object properties and CSS properties. When these are ambiguous they are qualified as object properties and CSS properties respectively.
Generally, when the specification states that a feature applies to the HTML syntax or the XHTML syntax, it also includes the other. When a feature specifically only applies to one of the two languages, it is called out by explicitly stating that it does not apply to the other format, as in "for HTML, ... (this does not apply to XHTML)".
This specification uses the term document to refer to any use
of HTML, ranging from short static documents to long essays or reports with rich multimedia, as
well as to fully-fledged interactive applications. The term is used to refer both to Document
objects and their descendant DOM trees, and to serialized byte streams using the HTML syntax or XHTML syntax, depending on context.
In the context of the DOM structures, the terms HTML document and XML document are used as defined in the DOM specification, and refer specifically to
two different modes that Document
objects can find themselves in. [DOM] (Such uses are
always hyperlinked to their definition.)
In the context of byte streams, the term HTML document refers to resources labeled as text/html
, and the term XML document refers to
resources labeled with an XML MIME type.
The term XHTML document is used to refer to both Documents in the XML document mode that contains element nodes in the HTML namespace, and byte streams labeled with an XML MIME type that contain elements from the HTML namespace, depending on context.
For simplicity, terms such as shown, displayed, and visible might sometimes be used when referring to the way a document is rendered to the user. These terms are not meant to imply a visual medium; they must be considered to apply to other media in equivalent ways.
When an algorithm B says to return to another algorithm A, it implies that A called B. Upon returning to A, the implementation must continue from where it left off in calling B. Some algorithms run in parallel; this means that the algorithm’s subsequent steps are to be run, one after another, at the same time as other logic in the specification (e.g., at the same time as the event loop). This specification does not define the precise mechanism by which this is achieved, be it time-sharing cooperative multitasking, fibers, threads, processes, using different hyperthreads, cores, CPUs, machines, etc. By contrast, an operation that is to run immediately must interrupt the currently running task, run itself, and then resume the previously running task.
The term "transparent black" refers to the color with red, green, blue, and alpha channels all set to zero.
2.1.1. Resources
The specification uses the term supported when referring to whether a user agent has an implementation capable of decoding the semantics of an external resource. A format or type is said to be supported if the implementation can process an external resource of that format or type without critical aspects of the resource being ignored. Whether a specific resource is supported can depend on what features of the resource’s format are in use.
For example, a PNG image would be considered to be in a supported format if its pixel data could be decoded and rendered, even if, unbeknownst to the implementation, the image also contained animation data.
An MPEG-4 video file would not be considered to be in a supported format if the compression format used was not supported, even if the implementation could determine the dimensions of the movie from the file’s metadata.
What some specifications, in particular the HTTP specification, refer to as a representation is referred to in this specification as a resource. [HTTP]
The term MIME type is used to refer to what is sometimes called an Internet media type in protocol literature. The term media type in this specification is used to refer to the type of media intended for presentation, as used by the CSS specifications. [RFC2046] [MEDIAQ]
A string is a valid MIME type if it matches the media-type
rule. In particular, a valid MIME type may include MIME type parameters. [HTTP]
A string is a valid MIME type with no parameters if it matches the media-type
rule, but does not contain any U+003B SEMICOLON
characters (;). In other words, if it consists only of a type and subtype, with no MIME Type
parameters. [HTTP]
The term HTML MIME type is used to refer to the MIME type text/html
.
A resource’s critical subresources are those that the resource needs to have available to be correctly processed. Which resources are considered critical or not is defined by the specification that defines the resource’s format.
2.1.2. XML compatibility
To ease migration from HTML to XHTML, user agents conforming to this specification will place
elements in HTML in the http://www.w3.org/1999/xhtml
namespace, at least for the
purposes of the DOM and CSS. The term "HTML elements",
when used in this specification, refers to any element in that namespace, and thus refers to both
HTML and XHTML elements.
Except where otherwise stated, all elements defined or mentioned in this specification are in the HTML namespace ("http://www.w3.org/1999/xhtml
"), and all attributes defined or
mentioned in this specification have no namespace.
The term element type is used to refer to the set of elements that have
a given local name and namespace. For example, button
elements are elements with the element
type button
, meaning they have the local name "button
" and (implicitly as
defined above) the HTML namespace.
Attribute names are said to be XML-compatible if they match the Name
production defined in XML and they contain no U+003A COLON
characters (:). [XML]
The term XML MIME type is used to refer to the MIME types text/xml
, application/xml
, and any MIME type whose subtype ends
with the four characters "+xml
". [RFC7303]
2.1.3. DOM trees
When it is stated that some element or attribute is ignored, or treated as some other value, or handled as if it was something else, this refers only to the processing of the node after it is in the DOM. A user agent must not mutate the DOM in such situations.
A content attribute is said to change value only if its new value is different than its previous value; setting an attribute to a value it already has does not change it.
The term empty, when used for an attribute value, Text
node, or
string means that the length of the text is zero (i.e., not even containing spaces or control
characters).
An element’s child text content is the concatenation of the data of all the Text
nodes that are children of the element (ignoring any other nodes such as
comments or elements), in tree order.
A node A is inserted into a node B when the insertion steps are invoked with A as the argument and A’s new parent is B. Similarly, a node A is removed from a node B when the removing steps are invoked with A as the removedNode argument and B as the oldParent argument.
A node is inserted into a document when the insertion steps are invoked with it as the argument and it is now in a document tree. Analogously, a node is removed from a document when the removing steps are invoked with it as the argument and it is now no longer in a document tree.
2.1.4. Scripting
The construction "a Foo
object", where Foo
is actually an interface,
is sometimes used instead of the more accurate "an object implementing the interface Foo
".
An IDL attribute is said to be getting when its value is being retrieved (e.g., by author script), and is said to be setting when a new value is assigned to it.
If a DOM object is said to be live, then the attributes and methods on that object must operate on the actual underlying data, not a snapshot of the data.
In the contexts of events, the terms fire and dispatch are used as defined in the
DOM specification: firing an event means to create and dispatch it, and dispatching an event means to follow the steps that propagate the event through the
tree. The term trusted event is used to refer to events whose isTrusted
attribute is initialized to true. [DOM]
2.1.5. Plugins
The term plugin refers to a user-agent defined set of content
handlers that can be used by the user agent. The content handlers can take part in the user
agent’s rendering of a Document
object, but that neither act as child browsing contexts of the Document
nor introduce any Node
objects to the Document
's DOM.
Typically such content handlers are provided by third parties, though a user agent can also designate built-in content handlers as plugins.
A user agent must not consider the types text/plain
and application/octet-stream
as having a registered plugin.
One example of a plugin would be a PDF viewer that is instantiated in a browsing context when the user navigates to a PDF file. This would count as a plugin regardless of whether the party that implemented the PDF viewer component was the same as that which implemented the user agent itself. However, a PDF viewer application that launches separate from the user agent (as opposed to using the same interface) is not a plugin by this definition.
This specification does not define a mechanism for interacting with plugins, as it is expected to be user-agent- and platform-specific. Some user agents might opt to support a plugin mechanism such as the Netscape Plugin API; others might use remote content converters or have built-in support for certain types. Indeed, this specification doesn’t require user agents to support plugins at all. [NPAPI]
A plugin can be secured if it honors the semantics of the sandbox
attribute.
For example, a secured plugin would prevent its contents from creating pop-up windows when the
plugin is instantiated inside a sandboxed iframe
.
Browsers should take extreme care when interacting with external content intended for plugins. When third-party software is run with the same privileges as the user agent itself, vulnerabilities in the third-party software become as dangerous as if they were vulnerabilities of the user agent itself.
Since different users having different sets of plugins provides a fingerprinting vector that increases the chances of users being uniquely identified, user agents are encouraged to support the exact same set of plugins for each user.
2.1.6. Character encodings
A character encoding, or just encoding where that is not ambiguous, is a defined way to convert between byte streams and Unicode strings, as defined in the WHATWG Encoding specification. An encoding has an encoding name and one or more encoding labels, referred to as the encoding’s name and labels in the Encoding specification. [ENCODING]
A UTF-16 encoding is UTF-16BE or UTF-16LE. [ENCODING]
An ASCII-compatible encoding is any encoding that is not a UTF-16 encoding. [ENCODING]
Since support for encodings that are not defined in the WHATWG Encoding specification is prohibited, UTF-16 encodings are the only encodings that this specification needs to treat as not being ASCII-compatible encodings.
The term code unit is used as defined in the Web IDL specification: a 16
bit unsigned integer, the smallest atomic component of a DOMString
. (This is a
narrower definition than the one used in Unicode, and is not the same as a code point.) [WEBIDL]
The term Unicode code point means a Unicode scalar value where possible, and an isolated surrogate code point when not. When a conformance requirement is defined in terms of characters or Unicode code points, a pair of code units consisting of a high surrogate followed by a low surrogate must be treated as the single code point represented by the surrogate pair, but isolated surrogates must each be treated as the single code point with the value of the surrogate. [UNICODE]
In this specification, the term character, when not qualified as Unicode character, is synonymous with the term Unicode code point.
The term Unicode character is used to mean a Unicode scalar value (i.e. any Unicode code point that is not a surrogate code point). [UNICODE]
The code-unit length of a string is the number of code units in that string.
This complexity results from the historical decision to define the DOM API in terms of 16 bit (UTF-16) code units, rather than in terms of Unicode characters.
2.2. Conformance requirements
All diagrams, examples, and notes in this specification are non-normative, as are all sections explicitly marked non-normative. Everything else in this specification is normative.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in the normative parts of this document are to be interpreted as described in RFC2119. The key word "OPTIONALLY" in the normative parts of this document is to be interpreted with the same normative meaning as "MAY" and "OPTIONAL". For readability, these words do not appear in all uppercase letters in this specification. [RFC2119]
Requirements phrased in the imperative as part of algorithms (such as "strip any leading space characters" or "return false and abort these steps") are to be interpreted with the meaning of the key word ("must", "should", "may", etc) used in introducing the algorithm.
To eat an orange, the user must: 1. Peel the orange. 2. Separate each slice of the orange. 3. Eat the orange slices.
...it would be equivalent to the following:
To eat an orange: 1. The user must peel the orange. 2. The user must separate each slice of the orange. 3. The user must eat the orange slices.
Here the key word is "must".
The former (imperative) style is generally preferred in this specification for stylistic reasons.
Conformance requirements phrased as algorithms or specific steps may be implemented in any manner, so long as the end result is equivalent. (In particular, the algorithms defined in this specification are intended to be easy to follow, and not intended to be performant.)
2.2.1. Conformance classes
This specification describes the conformance criteria for user agents (relevant to implementors) and documents (relevant to authors and authoring tool implementors).
Conforming documents are those that comply with all the conformance criteria for documents. For readability, some of these conformance requirements are phrased as conformance requirements on authors; such requirements are implicitly requirements on documents: by definition, all documents are assumed to have had an author. (In some cases, that author may itself be a user agent — such user agents are subject to additional rules, as explained below.)
For example, if a requirement states that "authors must not use the foobar
element", it would imply that documents are not allowed to contain elements named foobar
.
There is no implied relationship between document conformance requirements and implementation conformance requirements. User agents are not free to handle non-conformant documents as they please; the processing model described in this specification applies to implementations regardless of the conformity of the input documents.
User agents fall into several (overlapping) categories with different conformance requirements.
- Web browsers and other interactive user agents
-
Web browsers that support the XHTML syntax must process elements and attributes from the HTML namespace found in XML documents as described in this specification, so that users can interact with them, unless the semantics of those elements have been overridden by other specifications.
A conforming XHTML processor would, upon finding an XHTML
script
element in an XML document, execute the script contained in that element. However, if the element is found within a transformation expressed in XSLT (assuming the user agent also supports XSLT), then the processor would instead treat thescript
element as an opaque element that forms part of the transform.Web browsers that support the HTML syntax must process documents labeled with an HTML MIME type as described in this specification, so that users can interact with them.
User agents that support scripting must also be conforming implementations of the IDL fragments in this specification, as described in the Web IDL specification. [WEBIDL]
Unless explicitly stated, specifications that override the semantics of HTML elements do not override the requirements on DOM objects representing those elements. For example, the
script
element in the example above would still implement theHTMLScriptElement
interface. - Non-interactive presentation user agents
-
User agents that process HTML and XHTML documents purely to render non-interactive versions of them must comply to the same conformance criteria as Web browsers, except that they are exempt from requirements regarding user interaction.
Typical examples of non-interactive presentation user agents are printers (static user agents) and overhead displays (dynamic user agents). It is expected that most static non-interactive presentation user agents will also opt to lack scripting support.
A non-interactive but dynamic presentation user agent would still execute scripts, allowing forms to be dynamically submitted, and so forth. However, since the concept of "focus" is irrelevant when the user cannot interact with the document, the user agent would not need to support any of the focus-related DOM APIs.
- Visual user agents that support the suggested default rendering
-
User agents, whether interactive or not, may be designated (possibly as a user option) as supporting the suggested default rendering defined by this specification.
This is not required. In particular, even user agents that do implement the suggested default rendering are encouraged to offer settings that override this default to improve the experience for the user, e.g., changing the color contrast, using different focus styles, or otherwise making the experience more accessible and usable to the user.
User agents that are designated as supporting the suggested default rendering must, while so designated, implement the rules in §10 Rendering. That section defines the behavior that user agents are expected to implement.
- User agents with no scripting support
-
Implementations that do not support scripting (or which have their scripting features disabled entirely) are exempt from supporting the events and DOM interfaces mentioned in this specification. For the parts of this specification that are defined in terms of an events model or in terms of the DOM, such user agents must still act as if events and the DOM were supported.
Scripting can form an integral part of an application. Web browsers that do not support scripting, or that have scripting disabled, might be unable to fully convey the author’s intent.
- Conformance checkers
-
Conformance checkers must verify that a document conforms to the applicable conformance criteria described in this specification. Automated conformance checkers are exempt from detecting errors that require interpretation of the author’s intent (for example, while a document is non-conforming if the content of a
blockquote
element is not a quote, conformance checkers running without the input of human judgement do not have to check thatblockquote
elements only contain quoted material).Conformance checkers must check that the input document conforms when parsed without a browsing context (meaning that no scripts are run, and that the parser’s scripting flag is disabled), and should also check that the input document conforms when parsed with a browsing context in which scripts execute, and that the scripts never cause non-conforming states to occur other than transiently during script execution itself. (This is only a "SHOULD" and not a "MUST" requirement because it has been proven to be impossible. [COMPUTABLE])
The term "HTML validator" can be used to refer to a conformance checker that itself conforms to the applicable requirements of this specification.
XML DTDs cannot express all the conformance requirements of this specification. Therefore, a validating XML processor and a DTD cannot constitute a conformance checker. Also, since neither of the two authoring formats defined in this specification are applications of SGML, a validating SGML system cannot constitute a conformance checker either.To put it another way, there are three types of conformance criteria:
-
Criteria that can be expressed in a DTD.
-
Criteria that cannot be expressed by a DTD, but can still be checked by a machine.
-
Criteria that can only be checked by a human.
A conformance checker must check for the first two. A simple DTD-based validator only checks for the first class of errors and is therefore not a conforming conformance checker according to this specification.
-
- Data mining tools
-
Applications and tools that process HTML and XHTML documents for reasons other than to either render the documents or check them for conformance should act in accordance with the semantics of the documents that they process.
A tool that generates document outlines but increases the nesting level for each paragraph and does not increase the nesting level for each section would not be conforming.
- Authoring tools and markup generators
-
Authoring tools and markup generators must generate conforming documents. Conformance criteria that apply to authors also apply to authoring tools, where appropriate.
Authoring tools are exempt from the strict requirements of using elements only for their specified purpose, but only to the extent that authoring tools are not yet able to determine author intent. However, authoring tools must not automatically misuse elements or encourage their users to do so.
For example, it is not conforming to use an
address
element for arbitrary contact information; that element can only be used for marking up contact information for the author of the document or section. However, since an authoring tool is likely unable to determine the difference, an authoring tool is exempt from that requirement. This does not mean, though, that authoring tools can useaddress
elements for any block of italics text (for instance); it just means that the authoring tool doesn’t have to verify, if a user inserts contact information for a section or something else.In terms of conformance checking, an editor has to output documents that conform to the same extent that a conformance checker will verify.
When an authoring tool is used to edit a non-conforming document, it may preserve the conformance errors in sections of the document that were not edited during the editing session (i.e., an editing tool is allowed to round-trip erroneous content). However, an authoring tool must not claim that the output is conformant if errors have been so preserved.
Authoring tools are expected to come in two broad varieties: tools that work from structure or semantic data, and tools that work on a What-You-See-Is-What-You-Get media-specific editing basis (WYSIWYG).
The former is the preferred mechanism for tools that author HTML, since the structure in the source information can be used to make informed choices regarding which HTML elements and attributes are most appropriate.
However, WYSIWYG tools are legitimate. WYSIWYG tools should use elements they know are appropriate, and should not use elements that they do not know to be appropriate. This might in certain extreme cases mean limiting the use of flow elements to just a few elements, like
div
,b
,i
, andspan
and making liberal use of thestyle
attribute.All authoring tools, whether WYSIWYG or not, should make a best effort attempt at enabling users to create well-structured, semantically rich, media-independent content.
User agents may impose implementation-specific limits on otherwise unconstrained inputs, e.g., to prevent denial of service attacks, to guard against running out of memory, or to work around platform-specific limitations.
For compatibility with existing content and prior specifications, this specification describes two authoring formats: one based on XML (referred to as the XHTML syntax), and one using a custom format inspired by SGML (referred to as the HTML syntax). Implementations must support at least one of these two formats, although supporting both is encouraged.
Some conformance requirements are phrased as requirements on elements, attributes, methods or objects. Such requirements fall into two categories: those describing content model restrictions, and those describing implementation behavior. Those in the former category are requirements on documents and authoring tools. Those in the second category are requirements on user agents. Similarly, some conformance requirements are phrased as requirements on authors; such requirements are to be interpreted as conformance requirements on the documents that authors produce. (In other words, this specification does not distinguish between conformance criteria on authors and conformance criteria on documents.)
2.2.2. Dependencies
This specification relies on several other underlying specifications.
- Unicode and Encoding
-
The Unicode character set is used to represent textual data, and the Encoding specification defines requirements around character encodings. [UNICODE]
This specification introduces terminology based on the terms defined in those specifications, as described earlier.
The following terms are used as defined in the Encoding specification: [ENCODING]
-
Getting an encoding
-
Get an output encoding
-
The generic decode algorithm which takes a byte stream and an encoding and returns a character stream
-
The UTF-8 decode algorithm which takes a byte stream and returns a character stream, additionally stripping one leading UTF-8 Byte Order Mark (BOM), if any
-
The UTF-8 decode without BOM algorithm which is identical to UTF-8 decode except that it does not strip one leading UTF-8 Byte Order Mark (BOM)
-
The UTF-8 decode without BOM or fail algorithm which is identical to UTF-8 decode without BOM except that it returns failure upon encountering an error
-
The encode algorithm which takes a character stream and an encoding and returns a byte stream
-
The UTF-8 encode algorithm which takes a character stream and returns a byte stream.
-
- XML and related specifications
-
Implementations that support the XHTML syntax must support some version of XML, as well as its corresponding namespaces specification, because that syntax uses an XML serialization with namespaces. [XML] [XML-NAMES]
The attribute with the tag name
xml:space
in the XML namespace is defined by the XML specification. [XML]This specification also references the
<?xml-stylesheet?>
processing instruction, defined in the Associating Style Sheets with XML documents specification. [XML-STYLESHEET]This specification also non-normatively mentions the
XSLTProcessor
interface and itstransformToFragment()
andtransformToDocument()
methods. [XSLTP] - URLs
-
The following terms are defined in the WHATWG URL specification: [URL]
-
Origin of URLs
-
The URL parser and basic URL parser as well as these parser states:
-
URL record, as well as its individual components:
-
The URL serializer
-
The host parser
-
The host serializer
-
The domain to Unicode algorithm
-
Parse errors from the URL parser
A number of schemes and protocols are referenced by this specification also:
-
The
data:
scheme [RFC2397] -
The
http:
scheme [HTTP] -
The
https:
scheme [HTTP] -
The
mailto:
scheme [RFC6068] -
The
sms:
scheme [RFC5724] -
The
urn:
scheme [URN]
Media fragment syntax is defined in the Media Fragments URI specification. [MEDIA-FRAGS]
- HTTP and related specifications
-
The following terms are defined in the HTTP specifications: [HTTP]
-
Accept
header -
Accept-Language
header -
Cache-Control
header -
Content-Disposition
header -
Content-Language
header -
Content-Length
header -
Last-Modified
header
The following terms are defined in the Cookie specification: [COOKIES]
-
cookie-string
The following term is defined in the Web Linking specification: [RFC5988]
-
- Fetch
-
The following terms are defined in the WHATWG Fetch specification: [FETCH]
-
the
RequestCredentials
enumeration -
response and its associated:
-
request and its associated:
-
The following terms are defined in Referrer Policy [REFERRERPOLICY]
- Web IDL
-
The IDL fragments in this specification must be interpreted as required for conforming IDL fragments, as described in the Web IDL specification. [WEBIDL]
The following terms are defined in the Web IDL specification:
-
Global environment associated with a platform object
-
Read only (when applied to arrays)
-
Converting between WebIDL types and JS types
The Web IDL specification also defines the following types that are used in Web IDL fragments in this specification:
The term throw in this specification is used as defined in the WebIDL specification. The following exception names are defined by WebIDL and used by this specification:
When this specification requires a user agent to create a
Date
object representing a particular time (which could be the special value Not-a-Number), the milliseconds component of that time, if any, must be truncated to an integer, and the time value of the newly createdDate
object must represent the resulting truncated time.For instance, given the time 23045 millionths of a second after 01:00 UTC on January 1st 2000, i.e., the time 2000-01-01T00:00:00.023045Z, then the
Date
object created representing that time would represent the same time as that created representing the time 2000-01-01T00:00:00.023Z, 45 millionths earlier. If the given time is NaN, then the result is aDate
object that represents a time value NaN (indicating that the object does not represent a specific instant of time). - JavaScript
-
Some parts of the language described by this specification only support JavaScript as the underlying scripting language. [ECMA-262]
The term "JavaScript" is used to refer to ECMA262, rather than the official term ECMAScript, since the term JavaScript is more widely known. Similarly, the MIME type used to refer to JavaScript in this specification is
text/javascript
, since that is the most commonly used type, despite it being an officially obsoleted type according to RFC 4329. [RFC4329]The following terms are defined in the JavaScript specification and used in this specification [ECMA-262]:
-
Well-Known Symbols, including:
-
@@hasInstance
-
@@isConcatSpreadable
-
@@toPrimitive
-
@@toStringTag
-
-
Well-Known Intrinsic Objects, including:
-
The FunctionBody production
-
The Module production
-
The Pattern production
-
The Script production
-
The Type notation
-
The Property Descriptor specification type
-
The Source Text Module Record specification type and its ModuleEvaluation and ModuleDeclarationInstantiation methods
-
The ArrayCreate abstract operation
-
The Call abstract operation
-
The Construct abstract operation
-
The CopyDataBlockBytes abstract operation
-
The CreateByteDataBlock abstract operation
-
The CreateDataProperty abstract operation
-
The DetachArrayBuffer abstract operation
-
The EnqueueJob abstract operation
-
The FunctionCreate abstract operation
-
The Get abstract operation
-
The GetActiveScriptOrModule abstract operation
-
The GetFunctionRealm abstract operation
-
The HasOwnProperty abstract operation
-
The HostEnsureCanCompileStrings abstract operation
-
The HostPromiseRejectionTracker abstract operation
-
The HostResolveImportedModule abstract operation
-
The InitializeHostDefinedRealm abstract operation
-
The IsAccessorDescriptor abstract operation
-
The IsCallable abstract operation
-
The IsConstructor abstract operation
-
The IsDataDescriptor abstract operation
-
The IsDetachedBuffer abstract operation
-
The NewObjectEnvironment abstract operation
-
The OrdinaryGetPrototypeOf abstract operation
-
The OrdinarySetPrototypeOf abstract operation
-
The OrdinaryIsExtensible abstract operation
-
The OrdinaryPreventExtensions abstract operation
-
The OrdinaryGetOwnProperty abstract operation
-
The OrdinaryDefineOwnProperty abstract operation
-
The OrdinaryGet abstract operation
-
The OrdinarySet abstract operation
-
The OrdinaryDelete abstract operation
-
The OrdinaryOwnPropertyKeys abstract operation
-
The ParseModule abstract operation
-
The ParseScript abstract operation
-
The RunJobs abstract operation
-
The SameValue abstract operation
-
The ScriptEvaluation abstract operation
-
The ToBoolean abstract operation
-
The ToString abstract operation
-
The ToUint32 abstract operation
-
The TypedArrayCreate abstract operation
-
The Abstract Equality Comparison algorithm
-
The Strict Equality Comparison algorithm
-
The
ArrayBuffer
object -
The
Date
object -
The
SyntaxError
object -
The
TypeError
object -
The
RangeError
object -
The
RegExp
object -
The typeof operator
- DOM
-
The Document Object Model (DOM) is a representation — a model — of a document and its content. The DOM is not just an API; the conformance criteria of HTML implementations are defined, in this specification, in terms of operations on the DOM. [DOM]
Implementations must support DOM and the events defined in UI Events, because this specification is defined in terms of the DOM, and some of the features are defined as extensions to the DOM interfaces. [DOM] [UIEVENTS]
In particular, the following features are defined in the DOM specification: [DOM]
-
Attr
interface -
Comment
interface -
DOMImplementation
interface -
Document
interface -
XMLDocument
interface -
DocumentFragment
interface -
DocumentType
interface -
DOMException
interface -
ChildNode
interface -
Element
interface -
Node
interface -
NodeList
interface -
ProcessingInstruction
interface -
Text
interface -
HTMLCollection
interface -
item()
method -
The terms collections and represented by the collection
-
DOMTokenList
interface -
createDocument()
method -
createHTMLDocument()
method -
createElement()
method -
createElementNS()
method -
getElementById()
method -
getElementsByClassName()
method -
appendChild()
method -
cloneNode()
method -
importNode()
method -
id
attribute -
textContent
attribute -
The tree concept
-
The tree order concept
-
The root concept
-
The inclusive ancestor concept
-
The document element concept
-
The in a document concept
-
The pre-insert, insert, append, remove, replace, and adopt algorithms for nodes
-
The insertion steps, removing steps, and adopting steps hooks
-
The attribute list concept.
-
The data of a text node.
-
Event
interface -
EventTarget
interface -
EventInit
dictionary type -
target
attribute -
currentTarget
attribute -
isTrusted
attribute -
initEvent()
method -
addEventListener()
method -
The
type
of an event -
The concept of an event listener and the event listeners associated with an
EventTarget
-
The encoding (herein the character encoding) and content type of a
Document
-
The distinction between XML documents and HTML documents
-
The terms quirks mode, limited-quirks mode, and no-quirks mode
-
The algorithm to clone a
Node
, and the concept of cloning steps used by that algorithm -
The concept of base URL change steps and the definition of what happens when an element is affected by a base URL change
-
The concept of an element’s unique identifier (ID)
-
The term supported tokens
-
The concept of a DOM range, and the terms start, end, and boundary point as applied to ranges.
-
The create an element algorithm
-
MutationObserver
interface and mutation observers in general
For example, to throw a
TimeoutError
exception, a user agent would construct a DOMException object whose type was the string "TimeoutError
" (and whose code was the number 23, for legacy reasons) and actually throw that object as an exception.The following features are defined in the UI Events specification: [UIEVENTS]
-
MouseEvent
interface and the following interface members:-
The
relatedTarget
attribute -
The
button
attribute -
The
ctrlKey
attribute -
The
shiftKey
attribute -
The
altKey
attribute -
The
metaKey
attribute -
The
getModifierState()
method
-
-
MouseEventInit
dictionary type -
The
FocusEvent
interface and itsrelatedTarget
attribute -
click event
-
dblclick event
-
mousedown event
-
mouseenter event
-
mouseleave event
-
mousemove event
-
mouseout event
-
mouseover event
-
mouseup event
-
wheel event
-
keydown event
-
keyup event
-
keypress event
The following features are defined in the Touch Events specification: [TOUCH-EVENTS]
-
Touch
interface -
Touch point concept
This specification sometimes uses the term name to refer to the event’s
type
; as in, "an event namedclick
" or "if the event name iskeypress
". The terms "name" and "type" for events are synonymous.The following features are defined in the DOM Parsing and Serialization specification: [DOM-PARSING]
The
Selection
interface is defined in the Selection API specification. [SELECTION-API]User agents are also encouraged to implement the features described in the HTML Editing APIs and
UndoManager
and DOM Transaction specifications. [EDITING] [UNDO]The following parts of the Fullscreen specification are referenced from this specification, in part to define the rendering of
dialog
elements, and also to define how the Fullscreen API interacts with the sandboxing features in HTML: [FULLSCREEN]-
The top layer concept
-
The fully exit fullscreen algorithm
The High Resolution Time specification provides the
DOMHighResTimeStamp
typedef and thePerformance
object’snow()
method. [HR-TIME-2] -
- File API
-
This specification uses the following features defined in the File API specification: [FILEAPI]
-
FileList
interface -
The concept of a
Blob
's snapshot state -
The concept of read errors
- Indexed Database API
-
This specification uses cleanup Indexed Database transactions defined by the Indexed Database API specification. [INDEXEDDB]
- Media Source Extensions
-
The following terms are defined in the Media Source Extensions specification: [MEDIA-SOURCE]
-
MediaSource
interface -
Detaching from a media element
-
- Media Capture and Streams
-
The following term is defined in the Media Capture and Streams specification: [MEDIACAPTURE-STREAMS]
-
MediaStream
interface
-
- XMLHttpRequest
-
This specification references the XMLHttpRequest specification to describe how the two specifications interact and to use its
ProgressEvent
features. The following features and terms are defined in the XMLHttpRequest specification: [XHR]-
XMLHttpRequest
interface -
XMLHttpRequest.responseXML
attribute -
ProgressEvent
interface -
ProgressEvent.lengthComputable
attribute -
ProgressEvent.loaded
attribute -
ProgressEvent.total
attribute
-
- Server-Sent Events
-
This specification references
EventSource
which is specified in the Server-Sent Events specification [EVENTSOURCE] - Media Queries
-
Implementations must support the Media Queries language. [MEDIAQ]
- CSS modules
-
While support for CSS as a whole is not required of implementations of this specification (though it is encouraged, at least for Web browsers), some features are defined in terms of specific CSS requirements.
In particular, some features require that a string be parsed as a CSS <color> value. When parsing a CSS value, user agents are required by the CSS specifications to apply some error handling rules. These apply to this specification also. [CSS3COLOR] [CSS-2015]
For example, user agents are required to close all open constructs upon finding the end of a style sheet unexpectedly. Thus, when parsing the string "
rgb(0,0,0
" (with a missing close-parenthesis) for a color value, the close parenthesis is implied by this error handling rule, and a value is obtained (the color black). However, the similar construct "rgb(0,0,
" (with both a missing parenthesis and a missing "blue" value) cannot be parsed, as closing the open construct does not result in a viable value.The following terms and features are defined in the CSS specification: [CSS-2015]
-
viewport
-
replaced element
-
intrinsic dimensions
The term named color is defined in the CSS Color specification. [CSS3COLOR]
The terms intrinsic width and intrinsic height refer to the width dimension and the height dimension, respectively, of intrinsic dimensions.
The term paint source is used as defined in the CSS Image Values and Replaced Content specification to define the interaction of certain HTML elements with the CSS 'element()' function. [CSS3-IMAGES]
The term default object size is also defined in the CSS Image Values and Replaced Content specification. [CSS3-IMAGES]
Implementations that support scripting must support the CSS Object Model. The following features and terms are defined in the CSSOM specifications: [CSSOM] [CSSOM-VIEW]
-
cssText
attribute ofCSSStyleDeclaration
-
CSS style sheets and their properties: type, location, parent CSS style sheet, owner node, owner CSS rule, media, title, alternate flag, disabled flag, CSS rules, origin-clean flag
-
Alternative style sheet sets and the preferred style sheet set
-
The
resize
event -
The
scroll
event
The following features and terms are defined in the CSS Syntax specifications: [CSS-SYNTAX-3]
The following terms are defined in the Selectors specification: [SELECTORS4]
The feature <length> is defined in the CSS Values and Units specification. [CSS-VALUES]
The term style attribute is defined in the CSS Style Attributes specification. [CSS-STYLE-ATTR]
The term used value is defined in the CSS Cascading and Inheritance specification. [CSS-CASCADE-3]
The
CanvasRenderingContext2D
object’s use of fonts depends on the features described in the CSS Fonts and Font Loading specifications, including in particularFontFace
objects and the font source concept. [CSS-FONTS-3] [CSS-FONT-LOADING-3]The following interface is defined in the Geometry Interfaces Module specification: [GEOMETRY-1]
-
DOMMatrix
interface
-
- SVG
-
The
CanvasRenderingContext2D
object’s use of fonts depends on the features described in the CSS Fonts and Font Loading specifications, including in particularFontFace
objects and the font source concept. [CSS-FONTS-3] [CSS-FONT-LOADING-3]The following interface is defined in the SVG specification: [SVG11]
- WebGL
-
The following interface is defined in the WebGL specification: [WEBGL]
- WebVTT
-
Implementations may support WebVTT as a text track format for subtitles, captions, chapter titles, metadata, etc, for media resources. [WEBVTT]
The following terms, used in this specification, are defined in the WebVTT specification:
- The WebSocket protocol
-
The following terms are defined in the WebSocket protocol specification: [RFC6455]
- ARIA
-
The
role
attribute is defined in the ARIA specification, as are the following roles: [wai-aria-1.1]alert
alertdialog
application
article
banner
button
cell
checkbox
columnheader
combobox
complementary
contentinfo
definition
dialog
directory
document
feed
figure
form
grid
gridcell
group
heading
img
link
list
listbox
listitem
log
main
marquee
math
menu
menubar
menuitem
menuitemcheckbox
menuitemradio
navigation
none
note
option
presentation
progressbar
radio
radiogroup
region
row
rowgroup
rowheader
scrollbar
search
searchbox
separator
slider
spinbutton
status
switch
tab
table
tablist
tabpanel
term
textbox
timer
toolbar
tooltip
tree
treegrid
treeitem
In addition, the following
aria-*
content attributes are defined in the ARIA specification: [wai-aria-1.1]aria-activedescendant
aria-atomic
aria-autocomplete
aria-busy
aria-checked
aria-colcount
aria-colindex
aria-colspan
aria-controls
aria-current
aria-describedby
aria-details
aria-dialog
aria-disabled
aria-dropeffect
aria-errormessage
aria-expanded
aria-flowto
aria-grabbed
aria-haspopup
aria-hidden
aria-invalid
aria-keyshortcuts
aria-label
aria-labelledby
aria-level
aria-live
aria-multiline
aria-multiselectable
aria-orientation
aria-owns
aria-placeholder
aria-posinset
aria-pressed
aria-readonly
aria-relevant
aria-required
aria-roledescription
aria-rowcount
aria-rowindex
aria-rowspan
aria-selected
aria-setsize
aria-sort
aria-valuemax
aria-valuemin
aria-valuenow
aria-valuetext
- Content Security Policy
-
The following terms are defined in Content Security Policy: [CSP3]
-
The parse a serialized Content Security Policy algorithm
-
The Initialize a global object’s CSP list algorithm
-
The Initialize a Document’s CSP list algorithm
-
The Should element’s inline behavior be blocked by Content Security Policy? algorithm
-
The
report-uri
,frame-ancestors
, andsandbox
directives -
The EnsureCSPDoesNotBlockStringCompilation abstract algorithm
-
The Is base allowed for Document? algorithm
-
The Should element be blocked a priori by Content Security Policy? algorithm
-
The following terms are defined in Content Security Policy: Document Features
- Service Workers
-
The following terms are defined in Service Workers: [SERVICE-WORKERS]
- Secure Contexts
-
The following term is defined in Secure Contexts: [SECURE-CONTEXTS]
- Payment Request API
-
The following term is defined in the Payment Request API specification: [PAYMENT-REQUEST]
-
PaymentRequest
interface
-
- MathML
-
While support for MathML as a whole is not required by this specification (though it is encouraged, at least for Web browsers), certain features depend upon small parts of MathML being implemented. [MATHML]
The following features are defined in the MathML specification:
- SVG
-
While support for SVG as a whole is not required by this specification (though it is encouraged, at least for Web browsers), certain features depend upon parts of SVG being implemented.
Also, the SVG specifications do not reflect implementation reality. Implementations implement subsets of SVG 1.1 and SVG Tiny 1.2. Although it is hoped that the in-progress SVG 2 specification is a more realistic target for implementations, until that specification is ready, user agents that implement SVG must do so with the following willful violations and additions. [SVG11] [SVGTINY12] [SVG2]
User agents that implement SVG must not implement the following features from SVG 1.1:
-
The
tref
element -
The
cursor
element (use CSS’scursor
property instead) -
The font-defining SVG elements:
font
,glyph
,missing-glyph
,hkern
,vkern
,font-face
,font-face-src
,font-face-uri
,font-face-format
, andfont-face-name
(use CSS’s@font-face
instead) -
The
externalResourcesRequired
attribute -
The
enable-background
property -
The
contentScriptType
andcontentStyleType
attributes (use thetype
attribute on the SVGscript
andstyle
elements instead)
User agents that implement SVG must implement the following features from SVG Tiny 1.2:
-
The
non-scaling-stroke
value for thevector-effect
property -
The
class
attribute is allowed on all SVG elements -
The
tabindex
attribute is allowed on visible SVG elements -
The ARIA accessibility attributes are allowed on all SVG elements
The following features are defined in the SVG specifications:
-
SVGScriptElement
interface -
SVG
desc
element -
SVG
foreignObject
element -
SVG
script
element -
SVG
svg
element -
SVG
title
element
-
- Filter Effects
-
The following feature is defined in the Filter Effects specification:
This specification does not require support of any particular network protocol, style sheet language, scripting language, or any of the DOM specifications beyond those required in the list above. However, the language described by this specification is biased towards CSS as the styling language, JavaScript as the scripting language, and HTTP as the network protocol, and several features assume that those languages and protocols are in use.
A user agent that implements the HTTP protocol must implement the Web Origin Concept specification and the HTTP State Management Mechanism specification (Cookies) as well. [HTTP] [ORIGIN] [COOKIES]
This specification might have certain additional requirements on character encodings, image formats, audio formats, and video formats in the respective sections.
2.2.3. Extensibility
Vendor-specific proprietary user agent extensions to this specification are strongly discouraged. Documents must not use such extensions, as doing so reduces interoperability and fragments the user base, allowing only users of specific user agents to access the content in question.
If such extensions are nonetheless needed, e.g., for experimental purposes, then vendors are strongly urged to use one of the following extension mechanisms:
-
For markup-level features that can be limited to the XML serialization and need not be supported in the HTML serialization, vendors should use the namespace mechanism to define custom namespaces in which the non-standard elements and attributes are supported.
-
For markup-level features that are intended for use with the HTML syntax, extensions should be limited to new attributes of the form "
x-vendor-feature
", where vendor is a short string that identifies the vendor responsible for the extension, and feature is the name of the feature. New element names should not be created. Using attributes for such extensions exclusively allows extensions from multiple vendors to co-exist on the same element, which would not be possible with elements. Using the "x-vendor-feature
" form allows extensions to be made without risk of conflicting with future additions to the specification.For instance, a browser named "FerretBrowser" could use "ferret" as a vendor prefix, while a browser named "Mellblom Browser" could use "mb". If both of these browsers invented extensions that turned elements into scratch-and-sniff areas, an author experimenting with these features could write:<p>This smells of lemons! <span x-ferret-smellovision x-ferret-smellcode="LEM01" x-mb-outputsmell x-mb-smell="lemon juice"></span></p>
Attribute names beginning with the two characters "x-
" are reserved for
user agent use and are guaranteed to never be formally added to the HTML language. For
flexibility, attributes names containing underscores (the U+005F LOW LINE character) are also
reserved for experimental purposes and are guaranteed to never be formally added to the HTML
language.
Pages that use such attributes are by definition non-conforming.
For DOM extensions, e.g., new methods and IDL attributes, the new members should be prefixed by vendor-specific strings to prevent clashes with future versions of this specification.
For events, experimental event types should be prefixed with vendor-specific strings.
pleasold
" and
thus name the event "pleasoldgoingup
", possibly with an event handler attribute
named "onpleasoldgoingup
". All extensions must be defined so that the use of extensions neither contradicts nor causes the non-conformance of functionality defined in the specification.
fooTypeTime
" to a control’s DOM interface that returned
the time it took the user to select the current value of a control (say). On the other hand,
defining a new control that appears in a form’s elements
array would be in
violation of the above requirement, as it would violate the definition of elements
given in this specification. When adding new reflecting IDL attributes corresponding to content attributes of the form
"x-vendor-feature
", the IDL attribute should be named
"vendorFeature
" (i.e., the "x
" is dropped from
the IDL attribute’s name).
When vendor-neutral extensions to this specification are needed, either this specification can be updated accordingly, or an extension specification can be written that overrides the requirements in this specification. When someone applying this specification to their activities decides that they will recognize the requirements of such an extension specification, it becomes an applicable specification for the purposes of conformance requirements in this specification.
Someone could write a specification that defines any arbitrary byte stream as conforming, and then claim that their random junk is conforming. However, that does not mean that their random junk actually is conforming for everyone’s purposes: if someone else decides that the specification does not apply to their work, then they can quite legitimately say that the aforementioned random junk is just that, junk, and not conforming at all. As far as conformance goes, what matters in a particular community is what that community agrees is applicable.
applicable specification.
The conformance terminology for documents depends on the nature of the changes introduced by such applicable specifications, and on the content and intended interpretation of the document. Applicable specifications MAY define new document content (e.g., a foobar element), MAY prohibit certain otherwise conforming content (e.g., prohibit use of <table>s), or MAY change the semantics, DOM mappings, or other processing rules for content defined in this specification. Whether a document is or is not a conforming HTML document does not depend on the use of applicable specifications: if the syntax and semantics of a given conforming HTML document is unchanged by the use of applicable specification(s), then that document remains a conforming HTML document. If the semantics or processing of a given (otherwise conforming) document is changed by use of applicable specification(s), then it is not a conforming HTML document. For such cases, the applicable specifications SHOULD define conformance terminology.
As a suggested but not required convention, such specifications might define conformance terminology such as: "Conforming HTML+XXX document", where XXX is a short name for the applicable specification. (Example: "Conforming HTML+AutomotiveExtensions document").
a consequence of the rule given above is that certain syntactically correct HTML documents may not be conforming HTML documents in the presence of applicable specifications. (Example: the applicable specification defines <table> to be a piece of furniture — a document written to that specification and containing a <table> element is NOT a conforming HTML document, even if the element happens to be syntactically correct HTML.)
User agents must treat elements and attributes that they do not understand as semantically neutral; leaving them in the DOM (for DOM processors), and styling them according to CSS (for CSS processors), but not inferring any meaning from them.
When support for a feature is disabled (e.g., as an emergency measure to mitigate a security problem, or to aid in development, or for performance reasons), user agents must act as if they had no support for the feature whatsoever, and as if the feature was not mentioned in this specification. For example, if a particular feature is accessed via an attribute in a Web IDL interface, the attribute itself would be omitted from the objects that implement that interface — leaving the attribute on the object but making it return null or throw an exception is insufficient.
2.2.4. Interactions with XPath and XSLT
Implementations of XPath 1.0 that operate on HTML documents parsed or created in the
manners described in this specification (e.g., as part of the document.evaluate()
API)
must act as if the following edit was applied to the XPath 1.0 specification.
First, remove this paragraph:
A QName in the node test is expanded into an expanded-name using the namespace
declarations from the expression context. This is the same way expansion is done for element
type names in start and end-tags except that the default namespace declared with xmlns
is not used: if the QName does not have a prefix, then the namespace
URI is null (this is the same way attribute names are expanded). It is an error if the QName has a prefix for which there is no namespace declaration in the expression context.
Then, insert in its place the following:
A QName in the node test is expanded into an expanded-name using the namespace declarations from the expression context. If the QName has a prefix, then there must be a namespace declaration for this prefix in the expression context, and the corresponding namespace URI is the one that is associated with this prefix. It is an error if the QName has a prefix for which there is no namespace declaration in the expression context.If the QName has no prefix and the principal node type of the axis is element, then the default element namespace is used. Otherwise if the QName has no prefix, the namespace URI is null. The default element namespace is a member of the context for the XPath expression. The value of the default element namespace when executing an XPath expression through the DOM3 XPath API is determined in the following way:
If the context node is from an HTML DOM, the default element namespace is "http://www.w3.org/1999/xhtml".
Otherwise, the default element namespace URI is null.
This is equivalent to adding the default element namespace feature of XPath 2.0 to XPath 1.0, and using the HTML namespace as the default element namespace for HTML documents. It is motivated by the desire to have implementations be compatible with legacy HTML content while still supporting the changes that this specification introduces to HTML regarding the namespace used for HTML elements, and by the desire to use XPath 1.0 rather than XPath 2.0.
This change is a willful violation of the XPath 1.0 specification, motivated by desire to have implementations be compatible with legacy content while still supporting the changes that this specification introduces to HTML regarding which namespace is used for HTML elements. [XPATH]
XSLT 1.0 processors outputting to a DOM when the output method is "html" (either explicitly or via the defaulting rule in XSLT 1.0) are affected as follows:
If the transformation program outputs an element in no namespace, the processor must, prior to constructing the corresponding DOM element node, change the namespace of the element to the HTML namespace, ASCII-lowercase the element’s local name, and ASCII-lowercase the names of any non-namespaced attributes on the element.
This requirement is a willful violation of the XSLT 1.0 specification, required because this specification changes the namespaces and case-sensitivity rules of HTML in a manner that would otherwise be incompatible with DOM-based XSLT transformations. (Processors that serialize the output are unaffected.) [XSLT]
This specification does not specify precisely how XSLT processing interacts with the HTML parser infrastructure (for example, whether an XSLT processor acts as if it puts any
elements into a stack of open elements). However, XSLT processors must stop parsing if they successfully complete, and must set the current document readiness first to
"interactive
" and then to "complete
" if they are aborted.
This specification does not specify how XSLT interacts with the navigation algorithm, how it fits in with the event loop, nor how error pages are to be handled (e.g., whether XSLT errors are to replace an incremental XSLT output, or are rendered inline, etc).
There are also additional non-normative comments regarding the interaction of XSLT and HTML in the script
element section,
and of XSLT, XPath, and HTML in the template
element section.
2.3. Case-sensitivity and string comparison
Comparing two strings in a case-sensitive manner means comparing them exactly, code point for code point.
Comparing two strings in an ASCII case-insensitive manner means comparing them exactly, code point for code point, except that the characters in the range U+0041 to U+005A (i.e., LATIN CAPITAL LETTER A to LATIN CAPITAL LETTER Z) and the corresponding characters in the range U+0061 to U+007A (i.e., LATIN SMALL LETTER A to LATIN SMALL LETTER Z) are considered to also match.
Comparing two strings in a compatibility caseless manner means using the Unicode compatibility caseless match operation to compare the two strings, with no language-specific tailorings. [UNICODE]
Except where otherwise stated, string comparisons must be performed in a case-sensitive manner.
Converting a string to ASCII uppercase means replacing all characters in the range U+0061 to U+007A (i.e., LATIN SMALL LETTER A to LATIN SMALL LETTER Z) with the corresponding characters in the range U+0041 to U+005A (i.e., LATIN CAPITAL LETTER A to LATIN CAPITAL LETTER Z).
Converting a string to ASCII lowercase means replacing all characters in the range U+0041 to U+005A (i.e., LATIN CAPITAL LETTER A to LATIN CAPITAL LETTER Z) with the corresponding characters in the range U+0061 to U+007A (i.e., LATIN SMALL LETTER A to LATIN SMALL LETTER Z).
A string pattern is a prefix match for a string s when pattern is not longer than s and truncating s to pattern’s length leaves the two strings as matches of each other.
2.4. Common microsyntaxes
There are various places in HTML that accept particular data types, such as dates or numbers. This section describes what the conformance criteria for content in those formats is, and how to parse them.
Implementors are strongly urged to carefully examine any third-party libraries they might consider using to implement the parsing of syntaxes described below. For example, date libraries are likely to implement error handling behavior that differs from what is required in this specification, since error-handling behavior is often not defined in specifications that describe date syntaxes similar to those used in this specification, and thus implementations tend to vary greatly in how they handle errors.
2.4.1. Common parser idioms
The space characters, for the purposes of this specification, are U+0020 SPACE, U+0009 CHARACTER TABULATION (tab), U+000A LINE FEED (LF), U+000C FORM FEED (FF), and U+000D CARRIAGE RETURN (CR).
The White_Space characters are those that have the Unicode property "White_Space" in
the Unicode PropList.txt
data file. [UNICODE]
This should not be confused with the "White_Space" value (abbreviated "WS") of the "Bidi_Class"
property in the Unicode.txt
data file.
The control characters are those whose Unicode "General_Category" property has the
value "Cc" in the Unicode UnicodeData.txt
data file. [UNICODE]
The uppercase ASCII letters are the characters in the range U+0041 LATIN CAPITAL LETTER A to U+005A LATIN CAPITAL LETTER Z.
The lowercase ASCII letters are the characters in the range U+0061 LATIN SMALL LETTER A to U+007A LATIN SMALL LETTER Z.
The ASCII letters are the characters that are either uppercase ASCII letters or lowercase ASCII letters.
The ASCII digits are the characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9).
The alphanumeric ASCII characters are those that are either uppercase ASCII letters, lowercase ASCII letters, or ASCII digits.
The ASCII hex digits are the characters in the ranges U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9), U+0041 LATIN CAPITAL LETTER A to U+0046 LATIN CAPITAL LETTER F, and U+0061 LATIN SMALL LETTER A to U+0066 LATIN SMALL LETTER F.
The uppercase ASCII hex digits are the characters in the ranges U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9) and U+0041 LATIN CAPITAL LETTER A to U+0046 LATIN CAPITAL LETTER F only.
The lowercase ASCII hex digits are the characters in the ranges U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9) and U+0061 LATIN SMALL LETTER A to U+0066 LATIN SMALL LETTER F only.
Some of the micro-parsers described below follow the pattern of having an input variable that holds the string being parsed, and having a position variable pointing at the next character to parse in input.
For parsers based on this pattern, a step that requires the user agent to collect a sequence of characters means that the following algorithm must be run, with characters being the set of characters that can be collected:
-
Let input and position be the same variables as those of the same name in the algorithm that invoked these steps.
-
Let result be the empty string.
-
While position doesn’t point past the end of input and the character at position is one of the characters, append that character to the end of result and advance position to the next character in input.
-
Return result.
The step skip white space means that the user agent must collect a sequence of characters that are space characters. The collected characters are not used.
When a user agent is to strip line breaks from a string, the user agent must remove any U+000A LINE FEED (LF) and U+000D CARRIAGE RETURN (CR) characters from that string.
When a user agent is to strip leading and trailing white space from a string, the user agent must remove all space characters that are at the start or end of the string.
When a user agent is to strip and collapse white space in a string, it must replace any sequence of one or more consecutive space characters in that string with a single U+0020 SPACE character, and then strip leading and trailing white space from that string.
When a user agent has to strictly split a string on a particular delimiter character delimiter, it must use the following algorithm:
-
Let input be the string being parsed.
-
Let position be a pointer into input, initially pointing at the start of the string.
-
Let tokens be an ordered list of tokens, initially empty.
-
While position is not past the end of input:
-
Collect a sequence of characters that are not the delimiter character.
-
Append the string collected in the previous step to tokens.
-
Advance position to the next character in input.
-
-
Return tokens.
For the special cases of splitting a string on spaces and on commas, this algorithm does not apply (those algorithms also perform white space trimming).
2.4.2. Boolean attributes
A number of attributes are boolean attributes. The presence of a boolean attribute on an element represents the true value, and the absence of the attribute represents the false value.
If the attribute is present, its value must either be the empty string or a value that is an ASCII case-insensitive match for the attribute’s canonical name, with no leading or trailing white space.
A boolean attribute without a value assigned to it (e.g. checked) is implicitly equivalent to one that has the empty string assigned to it (i.e. checked=""). As a consequence, it represents the true value.
The values "true" and "false" are not allowed on boolean attributes. To represent a false value, the attribute has to be omitted altogether.
checked
and disabled
attributes are the boolean attributes.
<label><input type=checkbox checked name=cheese disabled> Cheese</label>
This could be equivalently written as this:
<label><input type=checkbox checked=checked name=cheese disabled=disabled> Cheese</label>
You can also mix styles; the following is still equivalent:
<label><input type='checkbox' checked name=cheese disabled=""> Cheese</label>
2.4.3. Keywords and enumerated attributes
Some attributes are defined as taking one of a finite set of keywords. Such attributes are called enumerated attributes. The keywords are each defined to map to a particular state (several keywords might map to the same state, in which case some of the keywords are synonyms of each other; additionally, some of the keywords can be said to be non-conforming, and are only in the specification for historical reasons). In addition, two default states can be given. The first is the invalid value default, the second is the missing value default.
If an enumerated attribute is specified, the attribute’s value must be an ASCII case-insensitive match for one of the given keywords that are not said to be non-conforming, with no leading or trailing white space.
When the attribute is specified, if its value is an ASCII case-insensitive match for one of the given keywords then that keyword’s state is the state that the attribute represents. If the attribute value matches none of the given keywords, but the attribute has an invalid value default, then the attribute represents that state. Otherwise, if the attribute value matches none of the keywords but there is a missing value default state defined, then that is the state represented by the attribute. Otherwise, there is no default, and invalid values mean that there is no state represented.
When the attribute is not specified, if there is a missing value default state defined, then that is the state represented by the (missing) attribute. Otherwise, the absence of the attribute means that there is no state represented.
The empty string can be a valid keyword.
2.4.4. Numbers
2.4.4.1. Signed integers
A string is a valid integer if it consists of one or more ASCII digits, optionally prefixed with a U+002D HYPHEN-MINUS character (-).
A valid integer without a U+002D HYPHEN-MINUS (-) prefix represents the number that is represented in base ten by that string of digits. A valid integer with a U+002D HYPHEN-MINUS (-) prefix represents the number represented in base ten by the string of digits that follows the U+002D HYPHEN-MINUS, subtracted from zero.
The rules for parsing integers are as given in the following algorithm. When invoked, the steps must be followed in the order given, aborting at the first step that returns a value. This algorithm will return either an integer or an error.
-
Let input be the string being parsed.
-
Let position be a pointer into input, initially pointing at the start of the string.
-
Let sign have the value "positive".
-
If position is past the end of input, return an error.
-
If the character indicated by position (the first character) is a U+002D HYPHEN-MINUS character (-):
-
Let sign be "negative".
-
Advance position to the next character.
-
If position is past the end of input, return an error.
Otherwise, if the character indicated by position (the first character) is a U+002B PLUS SIGN character (+):
-
Advance position to the next character. (The "
+
" is ignored, but it is not conforming.) -
If position is past the end of input, return an error.
-
-
If the character indicated by position is not an ASCII digit, then return an error.
-
Collect a sequence of characters that are ASCII digits, and interpret the resulting sequence as a base-ten integer. Let value be that integer.
-
If sign is "positive", return value, otherwise return the result of subtracting value from zero.
2.4.4.2. Non-negative integers
A string is a valid non-negative integer if it consists of one or more ASCII digits.
A valid non-negative integer represents the number that is represented in base ten by that string of digits.
The rules for parsing non-negative integers are as given in the following algorithm. When invoked, the steps must be followed in the order given, aborting at the first step that returns a value. This algorithm will return either zero, a positive integer, or an error.
-
Let input be the string being parsed.
-
Let value be the result of parsing input using the rules for parsing integers.
-
If value is an error, return an error.
-
If value is less than zero, return an error.
-
Return value.
2.4.4.3. Floating-point numbers
A string is a valid floating-point number if it consists of:
-
Optionally, a U+002D HYPHEN-MINUS character (-).
-
One or both of the following, in the given order:
-
A series of one or more ASCII digits.
-
Both of the following, in the given order:
-
A single U+002E FULL STOP character (.).
-
A series of one or more ASCII digits.
-
-
-
Optionally:
-
Either a U+0065 LATIN SMALL LETTER E character (e) or a U+0045 LATIN CAPITAL LETTER E character (E).
-
Optionally, a U+002D HYPHEN-MINUS character (-) or U+002B PLUS SIGN character (+).
-
A series of one or more ASCII digits.
-
A valid floating-point number represents the number obtained by multiplying the significand by ten raised to the power of the exponent, where the significand is the first number, interpreted as base ten (including the decimal point and the number after the decimal point, if any, and interpreting the significand as a negative number if the whole string starts with a U+002D HYPHEN-MINUS character (-) and the number is not zero), and where the exponent is the number after the E, if any (interpreted as a negative number if there is a U+002D HYPHEN-MINUS character (-) between the E and the number and the number is not zero, or else ignoring a U+002B PLUS SIGN character (+) between the E and the number if there is one). If there is no E, then the exponent is treated as zero.
The Infinity and Not-a-Number (NaN) values are not valid floating-point numbers.
The best representation of the number n as a floating-point number is the string obtained from running ToString(n). The abstract operation ToString is not uniquely determined. When there are multiple possible strings that could be obtained from ToString for a particular value, the user agent must always return the same string for that value (though it may differ from the value used by other user agents).
The rules for parsing floating-point number values are as given in the following algorithm. This algorithm must be aborted at the first step that returns something. This algorithm will return either a number or an error.
-
Let input be the string being parsed.
-
Let position be a pointer into input, initially pointing at the start of the string.
-
Let value have the value 1.
-
Let divisor have the value 1.
-
Let exponent have the value 1.
-
If position is past the end of input, return an error.
-
If the character indicated by position is a U+002D HYPHEN-MINUS character (-):
-
Change value and divisor to -1.
-
Advance position to the next character.
-
If position is past the end of input, return an error.
Otherwise, if the character indicated by position (the first character) is a U+002B PLUS SIGN character (+):
-
Advance position to the next character. (The "
+
" is ignored, but it is not conforming.) -
If position is past the end of input, return an error.
-
-
If the character indicated by position is a U+002E FULL STOP (.), and that is not the last character in input, and the character after the character indicated by position is an ASCII digit, then set value to zero and jump to the step labeled fraction.
-
If the character indicated by position is not an ASCII digit, then return an error.
-
Collect a sequence of characters that are ASCII digits, and interpret the resulting sequence as a base-ten integer. Multiply value by that integer.
-
If position is past the end of input, jump to the step labeled conversion.
-
Fraction: If the character indicated by position is a U+002E FULL STOP (.), run these substeps:
-
Advance position to the next character.
-
If position is past the end of input, or if the character indicated by position is not an ASCII digit, U+0065 LATIN SMALL LETTER E (e), or U+0045 LATIN CAPITAL LETTER E (E), then jump to the step labeled conversion.
-
If the character indicated by position is a U+0065 LATIN SMALL LETTER E character (e) or a U+0045 LATIN CAPITAL LETTER E character (E), skip the remainder of these substeps.
-
Fraction loop: Multiply divisor by ten.
-
Add the value of the character indicated by position, interpreted as a base-ten digit (0..9) and divided by divisor, to value.
-
Advance position to the next character.
-
If position is past the end of input, then jump to the step labeled conversion.
-
If the character indicated by position is an ASCII digit, jump back to the step labeled fraction loop in these substeps.
-
-
If the character indicated by position is a U+0065 LATIN SMALL LETTER E character (e) or a U+0045 LATIN CAPITAL LETTER E character (E), run these substeps:
-
Advance position to the next character.
-
If position is past the end of input, then jump to the step labeled conversion.
-
If the character indicated by position is a U+002D HYPHEN-MINUS character (-):
-
Change exponent to -1.
-
Advance position to the next character.
-
If position is past the end of input, then jump to the step labeled conversion.
Otherwise, if the character indicated by position is a U+002B PLUS SIGN character (+):
-
Advance position to the next character.
-
If position is past the end of input, then jump to the step labeled conversion.
-
-
If the character indicated by position is not an ASCII digit, then jump to the step labeled conversion.
-
Collect a sequence of characters that are ASCII digits, and interpret the resulting sequence as a base-ten integer. Multiply exponent by that integer.
-
Multiply value by ten raised to the exponentth power.
-
-
Conversion: Let S be the set of finite IEEE 754 double-precision floating-point values except -0, but with two special values added: 21024 and -21024.
-
Let rounded-value be the number in S that is closest to value, selecting the number with an even significand if there are two equally close values. (The two special values 21024 and -21024 are considered to have even significands for this purpose.)
-
If rounded-value is 21024 or -21024, return an error.
-
Return rounded-value.
2.4.4.4. Percentages and lengths
The rules for parsing dimension values are as given in the following algorithm. When invoked, the steps must be followed in the order given, aborting at the first step that returns a value. This algorithm will return either a number greater than or equal to 0.0, or an error; if a number is returned, then it is further categorized as either a percentage or a length.
-
Let input be the string being parsed.
-
Let position be a pointer into input, initially pointing at the start of the string.
-
If position is past the end of input, return an error.
-
If the character indicated by position is a U+002B PLUS SIGN character (+), advance position to the next character.
-
If position is past the end of input, return an error.
-
If the character indicated by position is not an ASCII digit, then return an error.
-
Collect a sequence of characters that are ASCII digits, and interpret the resulting sequence as a base-ten integer. Let value be that number.
-
If position is past the end of input, return value as a length.
-
If the character indicated by position is a U+002E FULL STOP character (.):
-
Advance position to the next character.
-
If position is past the end of input, or if the character indicated by position is not an ASCII digit, then return value as a length.
-
Let divisor have the value 1.
-
Fraction loop: Multiply divisor by ten.
-
Add the value of the character indicated by position, interpreted as a base-ten digit (0..9) and divided by divisor, to value.
-
Advance position to the next character.
-
If position is past the end of input, then return value as a length.
-
If the character indicated by position is an ASCII digit, return to the step labeled fraction loop in these substeps.
-
-
If position is past the end of input, return value as a length.
-
If the character indicated by position is a U+0025 PERCENT SIGN character (%), return value as a percentage.
-
Return value as a length.
2.4.4.5. Non-zero percentages and lengths
The rules for parsing non-zero dimension values are as given in the following algorithm. When invoked, the steps must be followed in the order given, aborting at the first step that returns a value. This algorithm will return either a number greater than 0.0, or an error; if a number is returned, then it is further categorized as either a percentage or a length.
-
Let input be the string being parsed.
-
Let value be the result of parsing input using the rules for parsing dimension values.
-
If value is an error, return an error.
-
If value is zero, return an error.
-
If value is a percentage, return value as a percentage.
-
Return value as a length.
2.4.4.6. Lists of floating-point numbers
A valid list of floating-point numbers is a number of valid floating-point numbers separated by U+002C COMMA characters, with no other characters (e.g. no space characters). In addition, there might be restrictions on the number of floating-point numbers that can be given, or on the range of values allowed.
The rules for parsing a list of floating-point numbers are as follows:
-
Let input be the string being parsed.
-
Let position be a pointer into input, initially pointing at the start of the string.
-
Let numbers be an initially empty list of floating-point numbers. This list will be the result of this algorithm.
-
Collect a sequence of characters that are space characters, U+002C COMMA, or U+003B SEMICOLON characters. This skips past any leading delimiters.
-
While position is not past the end of input:
-
Collect a sequence of characters that are not space characters, U+002C COMMA, U+003B SEMICOLON, ASCII digits, U+002E FULL STOP, or U+002D HYPHEN-MINUS characters. This skips past leading garbage.
-
Collect a sequence of characters that are not space characters, U+002C COMMA, or U+003B SEMICOLON characters, and let unparsed number be the result.
-
Let number be the result of parsing unparsed number using the rules for parsing floating-point number values.
-
If number is an error, set number to zero.
-
Append number to numbers.
-
Collect a sequence of characters that are space characters, U+002C COMMA, or U+003B SEMICOLON characters. This skips past the delimiter.
-
-
Return numbers.
2.4.4.7. Lists of dimensions
The rules for parsing a list of dimensions are as follows. These rules return a list of zero or more pairs consisting of a number and a unit, the unit being one of percentage, relative, and absolute.
-
Let raw input be the string being parsed.
-
If the last character in raw input is a U+002C COMMA character (,), then remove that character from raw input.
-
Split the string raw input on commas. Let raw tokens be the resulting list of tokens.
-
Let result be an empty list of number/unit pairs.
-
For each token in raw tokens, run the following substeps:
-
Let input be the token.
-
Let position be a pointer into input, initially pointing at the start of the string.
-
Let value be the number 0.
-
Let unit be absolute.
-
If position is past the end of input, set unit to relative and jump to the last substep.
-
If the character at position is an ASCII digit, collect a sequence of characters that are ASCII digits, interpret the resulting sequence as an integer in base ten, and increment value by that integer.
-
If the character at position is a U+002E FULL STOP character (.), run these substeps:
-
Collect a sequence of characters consisting of space characters and ASCII digits. Let s be the resulting sequence.
-
Remove all space characters in s.
-
If s is not the empty string, run these subsubsteps:
-
Let length be the number of characters in s (after the spaces were removed).
-
Let fraction be the result of interpreting s as a base-ten integer, and then dividing that number by 10length.
-
Increment value by fraction.
-
-
-
If the character at position is a U+0025 PERCENT SIGN character (%), then set unit to percentage.
Otherwise, if the character at position is a U+002A ASTERISK character (*), then set unit to relative.
-
Add an entry to result consisting of the number given by value and the unit given by unit.
-
-
Return the list result.
2.4.5. Dates and times
This means that encoded dates will look like 1582-03-01, 0033-03-27, or 2016-03-01, and date-times will look like 1929-11-13T19:00Z, 0325-06-03T00:21+10:30. The format is approximately YYYY-MM-DDTHH:MM:SS.DD±HH:MM, although some parts are optional, for example to express a month and day as in a birthday, a time without time-zone information, and the like.
Times are expressed using the 24-hour clock, and it is an error to express leap seconds.
Dates are expressed in the proleptic Gregorian calendar between the proleptic year 0000, and the year 9999. Other years cannot be encoded.
The proleptic Gregorian calendar is the calendar most common globally since around 1950, and is likely to be understood by almost everyone for dates between the years 1950 and 9999, and for many people for dates in the last few decades or centuries.
The Gregorian calendar was adopted officially in different countries at different times, between the years 1582 when it was proposed by Pope Gregory XIII as a replacement for the Julian calendar, and 1949 when it was adopted by the People’s republic of China.
For most practical purposes, dealing with the present, recent past, or the next few thousand years, this will work without problems. For dates before the adoption of the Gregorian Calendar - for example prior to 1917 in Russia or Turkey, prior to 1752 in Britain or the then British colonies of America, or prior to 1582 in Spain, the Spanish colonies in America, and the rest of the world, dates will not match those written at the time.
The use of the Gregorian calendar as an underlying encoding is a somewhat arbitrary choice. Many other calendars were or are in use, and the interested reader should look for information on the Web.
See also the discussion of date, time, and number formats in forms (for authors), implementation
notes regarding localization of form controls, and the time
element.
In the algorithms below, the number of days in month month of year year is: 31 if month is 1, 3, 5, 7, 8, 10, or 12; 30 if month is 4, 6, 9, or 11; 29 if month is 2 and year is a number divisible by 400, or if year is a number divisible by 4 but not by 100; and 28 otherwise. This takes into account leap years in the Gregorian calendar. [GREGORIAN]
When ASCII digits are used in the date and time syntaxes defined in this section, they express numbers in base ten.
While the formats described here are intended to be subsets of the corresponding ISO8601 formats, this specification defines parsing rules in much more detail than ISO8601. Implementors are therefore encouraged to carefully examine any date parsing libraries before using them to implement the parsing rules described below; ISO8601 libraries might not parse dates and times in exactly the same manner. [ISO8601]
Where this specification refers to the proleptic Gregorian calendar, it means the modern Gregorian calendar, extrapolated backwards to year 1. A date in the proleptic Gregorian calendar, sometimes explicitly referred to as a proleptic-Gregorian date, is one that is described using that calendar even if that calendar was not in use at the time (or place) in question. [GREGORIAN]
2.4.5.1. Months
A month consists of a specific proleptic-Gregorian date with no time-zone information and no date information beyond a year and a month. [GREGORIAN]
A string is a valid month string representing a year year and month month if it consists of the following components in the given order:
-
Four or more ASCII digits, representing year, where year > 0
-
A U+002D HYPHEN-MINUS character (-)
-
Two ASCII digits, representing the month month, in the range 1 ≤ month ≤ 12
For example, February 2005 is encoded 2005-02, and March of the year 33AD (as a proleptic
gregorian date) is encoded 0033-03
. The expression 325-03
does not mean March in the year 325, it is an error, because it does not have 4 digits for
the year.
The rules to parse a month string are as follows. This will return either a year and month, or nothing. If at any point the algorithm says that it "fails", this means that it is aborted at that point and returns nothing.
-
Let input be the string being parsed.
-
Let position be a pointer into input, initially pointing at the start of the string.
-
Parse a month component to obtain year and month. If this returns nothing, then fail.
-
If position is not beyond the end of input, then fail.
-
Return year and month.
The rules to parse a month component, given an input string and a position, are as follows. This will return either a year and a month, or nothing. If at any point the algorithm says that it "fails", this means that it is aborted at that point and returns nothing.
-
Collect a sequence of characters that are ASCII digits. If the collected sequence is not at least four characters long, then fail. Otherwise, interpret the resulting sequence as a base-ten integer. Let that number be the year.
-
If year is not a number greater than zero, then fail.
-
If position is beyond the end of input or if the character at position is not a U+002D HYPHEN-MINUS character, then fail. Otherwise, move position forwards one character.
-
Collect a sequence of characters that are ASCII digits. If the collected sequence is not exactly two characters long, then fail. Otherwise, interpret the resulting sequence as a base-ten integer. Let that number be the month.
-
If month is not a number in the range 1 ≤ month ≤ 12, then fail.
-
Return year and month.
2.4.5.2. Dates
A date consists of a specific proleptic-Gregorian date with no time-zone information, consisting of a year, a month, and a day. [GREGORIAN]
A string is a valid date string representing a year year, month month, and day day if it consists of the following components in the given order:
-
A valid month string, representing year and month
-
A U+002D HYPHEN-MINUS character (-)
-
Two ASCII digits, representing day, in the range 1 ≤ day ≤ maxday where maxday is the number of days in the month month and year year
For example, 29 February 2016 is encoded 2016-02-29, and 3 March of the year 33AD (as a
proleptic gregorian date) is encoded 0033-03-03
. The expression 325-03-03
does not mean 3 March in the year 325, it is an error, because
it does not have 4 digits for the year.
The rules to parse a date string are as follows. This will return either a date, or nothing. If at any point the algorithm says that it "fails", this means that it is aborted at that point and returns nothing.
-
Let input be the string being parsed.
-
Let position be a pointer into input, initially pointing at the start of the string.
-
Parse a date component to obtain year, month, and day. If this returns nothing, then fail.
-
If position is not beyond the end of input, then fail.
-
Let date be the date with year year, month month, and day day.
-
Return date.
The rules to parse a date component, given an input string and a position, are as follows. This will return either a year, a month, and a day, or nothing. If at any point the algorithm says that it "fails", this means that it is aborted at that point and returns nothing.
-
Parse a month component to obtain year and month. If this returns nothing, then fail.
-
Let maxday be the number of days in month month of year year.
-
If position is beyond the end of input or if the character at position is not a U+002D HYPHEN-MINUS character, then fail. Otherwise, move position forwards one character.
-
Collect a sequence of characters that are ASCII digits. If the collected sequence is not exactly two characters long, then fail. Otherwise, interpret the resulting sequence as a base-ten integer. Let that number be the day.
-
If day is not a number in the range 1 ≤ day ≤ maxday, then fail.
-
Return year, month, and day.
2.4.5.3. Yearless dates
A yearless date consists of a Gregorian month and a day within that month, but with no associated year. [GREGORIAN]
A string is a valid yearless date string representing a month month and a day day if it consists of the following components in the given order:
-
Optionally, two U+002D HYPHEN-MINUS characters (-)
-
Two ASCII digits, representing the month month, in the range 1 ≤ month ≤ 12
-
A U+002D HYPHEN-MINUS character (-)
-
Two ASCII digits, representing day, in the range 1 ≤ day ≤ maxday where maxday is the number of days in the month month and any arbitrary leap year (e.g., 4 or 2000)
In other words, if the month is "02
", meaning February, then the day can
be 29, as if the year was a leap year.
For example, 29 February is encoded 02-29
, and 3 March is encoded 03-03
.
The rules to parse a yearless date string are as follows. This will return either a month and a day, or nothing. If at any point the algorithm says that it "fails", this means that it is aborted at that point and returns nothing.
-
Let input be the string being parsed.
-
Let position be a pointer into input, initially pointing at the start of the string.
-
Parse a yearless date component to obtain month and day. If this returns nothing, then fail.
-
If position is not beyond the end of input, then fail.
-
Return month and day.
The rules to parse a yearless date component, given an input string and a position, are as follows. This will return either a month and a day, or nothing. If at any point the algorithm says that it "fails", this means that it is aborted at that point and returns nothing.
-
Collect a sequence of characters that are U+002D HYPHEN-MINUS characters (-). If the collected sequence is not exactly zero or two characters long, then fail.
-
Collect a sequence of characters that are ASCII digits. If the collected sequence is not exactly two characters long, then fail. Otherwise, interpret the resulting sequence as a base-ten integer. Let that number be the month.
-
If month is not a number in the range 1 ≤ month ≤ 12, then fail.
-
Let maxday be the number of days in month month of any arbitrary leap year (e.g., 4 or 2000).
-
If position is beyond the end of input or if the character at position is not a U+002D HYPHEN-MINUS character, then fail. Otherwise, move position forwards one character.
-
Collect a sequence of characters that are ASCII digits. If the collected sequence is not exactly two characters long, then fail. Otherwise, interpret the resulting sequence as a base-ten integer. Let that number be the day.
-
If day is not a number in the range 1 ≤ day ≤ maxday, then fail.
-
Return month and day.
2.4.5.4. Times
A time consists of a specific time with no time-zone information, consisting of an hour, a minute, a second, and a fraction of a second.
A string is a valid time string representing an hour hour, a minute minute, and a second second if it consists of the following components in the given order:
-
Two ASCII digits, representing hour, in the range 0 ≤ hour ≤ 23
-
A U+003A COLON character (:)
-
Two ASCII digits, representing minute, in the range 0 ≤ minute ≤ 59
-
If second is non-zero, or optionally if second is zero:
-
A U+003A COLON character (:)
-
Two ASCII digits, representing the integer part of second, in the range 0 ≤ s ≤ 59
-
If second is not an integer, or optionally if second is an integer:
-
A 002E FULL STOP character (.)
-
One, two, or three ASCII digits, representing the fractional part of second
-
-
The second component cannot be 60 or 61; leap seconds cannot be represented.
Times are encoded using the 24 hour clock, with optional seconds, and optional decimal fractions
of seconds. Thus 7.45pm is encoded as 19:45
. Note that parsing that time will return
19:45:00, or 7.45pm and zero seconds. 19:45:45.456
is 456 thousandths of
a second after 7.45pm and 45 seconds.
The rules to parse a time string are as follows. This will return either a time, or nothing. If at any point the algorithm says that it "fails", this means that it is aborted at that point and returns nothing.
-
Let input be the string being parsed.
-
Let position be a pointer into input, initially pointing at the start of the string.
-
Parse a time component to obtain hour, minute, and second. If this returns nothing, then fail.
-
If position is not beyond the end of input, then fail.
-
Let time be the time with hour hour, minute minute, and second second.
-
Return time.
The rules to parse a time component, given an input string and a position, are as follows. This will return either an hour, a minute, and a second, or nothing. If at any point the algorithm says that it "fails", this means that it is aborted at that point and returns nothing.
-
Collect a sequence of characters that are ASCII digits. If the collected sequence is not exactly two characters long, then fail. Otherwise, interpret the resulting sequence as a base-ten integer. Let that number be the hour.
-
If hour is not a number in the range 0 ≤ hour ≤ 23, then fail.
-
If position is beyond the end of input or if the character at position is not a U+003A COLON character, then fail. Otherwise, move position forwards one character.
-
Collect a sequence of characters that are ASCII digits. If the collected sequence is not exactly two characters long, then fail. Otherwise, interpret the resulting sequence as a base-ten integer. Let that number be the minute.
-
If minute is not a number in the range 0 ≤ minute ≤ 59, then fail.
-
Let second be a string with the value "0".
-
If position is not beyond the end of input and the character at position is a U+003A COLON, then run these substeps:
-
Advance position to the next character in input.
-
If position is beyond the end of input, or at the last character in input, or if the next two characters in input starting at position are not both ASCII digits, then fail.
-
Collect a sequence of characters that are either ASCII digits or U+002E FULL STOP characters. If the collected sequence is three characters long, or if it is longer than three characters long and the third character is not a U+002E FULL STOP character, or if it has more than one U+002E FULL STOP character, then fail. Otherwise, let second be the collected string.
-
-
Interpret second as a base-ten number (possibly with a fractional part). Let second be that number instead of the string version.
-
If second is not a number in the range 0 ≤ second < 60, then fail.
-
Return hour, minute, and second.
2.4.5.5. Floating dates and times
A floating date and time consists of a specific proleptic-Gregorian date, consisting of a year, a month, and a day, and a time, consisting of an hour, a minute, a second, and a fraction of a second, but expressed without a time zone. [GREGORIAN]
A string is a valid floating date and time string representing a date and time if it consists of the following components in the given order:
-
A valid date string representing the date
-
A U+0054 LATIN CAPITAL LETTER T character (T) or a U+0020 SPACE character
-
A valid time string representing the time
A string is a valid normalized floating date and time string representing a date and time if it consists of the following components in the given order:
-
A valid date string representing the date
-
A U+0054 LATIN CAPITAL LETTER T character (T)
-
A valid time string representing the time, expressed as the shortest possible string for the given time (e.g., omitting the seconds component entirely if the given time is zero seconds past the minute)
The rules to parse a floating date and time string are as follows. This will return either a date and time, or nothing. If at any point the algorithm says that it "fails", this means that it is aborted at that point and returns nothing.
-
Let input be the string being parsed.
-
Let position be a pointer into input, initially pointing at the start of the string.
-
Parse a date component to obtain year, month, and day. If this returns nothing, then fail.
-
If position is beyond the end of input or if the character at position is neither a U+0054 LATIN CAPITAL LETTER T character (T) nor a U+0020 SPACE character, then fail. Otherwise, move position forwards one character.
-
Parse a time component to obtain hour, minute, and second. If this returns nothing, then fail.
-
If position is not beyond the end of input, then fail.
-
Let date be the date with year year, month month, and day day.
-
Let time be the time with hour hour, minute minute, and second second.
-
Return date and time.
2.4.5.6. Time zones
A time-zone offset consists of a signed number of hours and minutes.
A string is a valid time-zone offset string representing a time-zone offset if it consists of either:
-
A U+005A LATIN CAPITAL LETTER Z character (Z), allowed only if the time zone is UTC
-
Or, the following components, in the given order:
-
Either a U+002B PLUS SIGN character (+) or, if the time-zone offset is not zero, a U+002D HYPHEN-MINUS character (-), representing the sign of the time-zone offset
-
Two ASCII digits, representing the hours component hour of the time-zone offset, in the range 0 ≤ hour ≤ 23
-
Optionally, a U+003A COLON character (:)
-
Two ASCII digits, representing the minutes component minute of the time-zone offset, in the range 0 ≤ minute ≤ 59
-
This format allows for time-zone offsets from -23:59 to +23:59. In practice, however, right now the range of offsets of actual time zones is -12:00 to +14:00, and the minutes component of offsets of actual time zones is always either 00, 30, or 45. There is no guarantee that this will remain so forever, however; time zones are changed by countries at will and do not follow a standard.
See also the usage notes and examples in the global date and time section below for details on using time-zone offsets with historical times that predate the formation of formal time zones.
The rules to parse a time-zone offset string are as follows. This will return either a time-zone offset, or nothing. If at any point the algorithm says that it "fails", this means that it is aborted at that point and returns nothing.
-
Let input be the string being parsed.
-
Let position be a pointer into input, initially pointing at the start of the string.
-
Parse a time-zone offset component to obtain timezonehours and timezoneminutes. If this returns nothing, then fail.
-
If position is not beyond the end of input, then fail.
-
Return the time-zone offset that is timezonehours hours and timezoneminutes minutes from UTC.
The rules to parse a time-zone offset component, given an input string and a position, are as follows. This will return either time-zone hours and time-zone minutes, or nothing. If at any point the algorithm says that it "fails", this means that it is aborted at that point and returns nothing.
-
If the character at position is a U+005A LATIN CAPITAL LETTER Z character (Z), then:
-
Let timezonehours be 0.
-
Let timezoneminutes be 0.
-
Advance position to the next character in input.
Otherwise, if the character at position is either a U+002B PLUS SIGN (+) or a U+002D HYPHEN-MINUS (-), then:
-
If the character at position is a U+002B PLUS SIGN (+), let sign be "positive". Otherwise, it’s a U+002D HYPHEN-MINUS (-); let sign be "negative".
-
Advance position to the next character in input.
-
Collect a sequence of characters that are ASCII digits. Let s be the collected sequence.
-
If s is exactly two characters long, then run these substeps:
-
Interpret s as a base-ten integer. Let that number be the timezonehours.
-
If position is beyond the end of input or if the character at position is not a U+003A COLON character, then fail. Otherwise, move position forwards one character.
-
Collect a sequence of characters that are ASCII digits. If the collected sequence is not exactly two characters long, then fail. Otherwise, interpret the resulting sequence as a base-ten integer. Let that number be the timezoneminutes.
If s is exactly four characters long, then run these substeps:
-
Interpret the first two characters of s as a base-ten integer. Let that number be the timezonehours.
-
Interpret the last two characters of s as a base-ten integer. Let that number be the timezoneminutes.
Otherwise, fail.
-
-
If timezonehours is not a number in the range 0 ≤ timezonehours ≤ 23, then fail.
-
If sign is "negative", then negate timezonehours.
-
If timezoneminutes is not a number in the range 0 ≤ timezoneminutes ≤ 59, then fail.
-
If sign is "negative", then negate timezoneminutes.
Otherwise, fail.
-
-
Return timezonehours and timezoneminutes.
2.4.5.7. Global dates and times
A global date and time consists of a specific proleptic-Gregorian date, consisting of a year, a month, and a day, and a time, consisting of an hour, a minute, a second, and a fraction of a second, expressed with a time-zone offset, consisting of a signed number of hours and minutes. [GREGORIAN]
A string is a valid global date and time string representing a date, time, and a time-zone offset if it consists of the following components in the given order:
-
A valid date string representing the date
-
A U+0054 LATIN CAPITAL LETTER T character (T) or a U+0020 SPACE character
-
A valid time string representing the time
-
A valid time-zone offset string representing the time-zone offset
Times in dates before the formation of UTC in the mid twentieth century must be expressed and interpreted in terms of UT1 (contemporary Earth mean solar time at the 0° longitude), not UTC (the approximation of UT1 that ticks in SI seconds). Time before the formation of time zones must be expressed and interpreted as UT1 times with explicit time zones that approximate the contemporary difference between the appropriate local time and the time observed at the location of Greenwich, London.
- "
0037-12-13 00:00Z
" -
Midnight in areas using London time on the birthday of Nero (the Roman Emperor). See below for further discussion on which date this actually corresponds to.
- "
1979-10-14T12:00:00.001-04:00
" -
One millisecond after noon on October 14th 1979, in the time zone in use on the east coast of the USA during daylight saving time.
- "
8592-01-01T02:09+02:09
" -
Midnight UTC on the 1st of January, 8592. The time zone associated with that time is two hours and nine minutes ahead of UTC, which is not currently a real time zone, but is nonetheless allowed.
Several things are notable about these dates:
-
Years with fewer than four digits have to be zero-padded. The date "37-12-13" would not be a valid date.
-
If the "
T
" is replaced by a space, it must be a single space character. The string "2001-12-21 12:00Z
" (with two spaces between the components) would not be parsed successfully. -
To unambiguously identify a moment in time prior to the introduction of the Gregorian calendar (insofar as moments in time before the formation of UTC can be unambiguously identified), the date has to be first converted to the Gregorian calendar from the calendar in use at the time (e.g., from the Julian calendar). The date of Nero’s birth is the 15th of December 37, in the Julian Calendar, which is the 13th of December 37 in the proleptic Gregorian calendar.
-
The time and time-zone offset components are not optional.
-
Dates before the year one can’t be represented as a datetime in this version of HTML.
-
Times of specific events in ancient times are, at best, approximations, since time was not well coordinated or measured until relatively recent decades.
-
Time-zone offsets differ based on daylight savings time.
The zone offset is not a complete time zone specification. When working with real date and time values, consider using a separate field for time zone, perhaps using IANA time zone IDs. [TIMEZONE]
A string is a valid normalized global date and time string representing a date, time, and a time-zone offset if it consists of the following components in the given order:
-
A valid date string representing the date converted to the UTC time zone
-
A U+0054 LATIN CAPITAL LETTER T character (T)
-
A valid time string representing the time converted to the UTC time zone and expressed as the shortest possible string for the given time (e.g., omitting the seconds component entirely if the given time is zero seconds past the minute)
-
A U+005A LATIN CAPITAL LETTER Z character (Z)
The rules to parse a global date and time string are as follows. This will return either a time in UTC, with associated time-zone offset information for round-tripping or display purposes, or nothing. If at any point the algorithm says that it "fails", this means that it is aborted at that point and returns nothing.
-
Let input be the string being parsed.
-
Let position be a pointer into input, initially pointing at the start of the string.
-
Parse a date component to obtain year, month, and day. If this returns nothing, then fail.
-
If position is beyond the end of input or if the character at position is neither a U+0054 LATIN CAPITAL LETTER T character (T) nor a U+0020 SPACE character, then fail. Otherwise, move position forwards one character.
-
Parse a time component to obtain hour, minute, and second. If this returns nothing, then fail.
-
If position is beyond the end of input, then fail.
-
Parse a time-zone offset component to obtain timezonehours and timezoneminutes. If this returns nothing, then fail.
-
If position is not beyond the end of input, then fail.
-
Let time be the moment in time at year year, month month, day day, hours hour, minute minute, second second, subtracting timezonehours hours and timezoneminutes minutes. That moment in time is a moment in the UTC time zone.
-
Let timezone be timezonehours hours and timezoneminutes minutes from UTC.
-
Return time and timezone.
2.4.5.8. Weeks
A week consists of a week-year number and a week number representing a seven-day period starting on a Monday. Each week-year in this calendaring system has either 52 or 53 such seven-day periods, as defined below. The seven-day period starting on the Gregorian date Monday December 29th 1969 (1969-12-29) is defined as week number 1 in week-year 1970. Consecutive weeks are numbered sequentially. The week before the number 1 week in a week-year is the last week in the previous week-year, and vice versa. [GREGORIAN]
A week-year with a number year has 53 weeks if it corresponds to either a year year in the proleptic Gregorian calendar that has a Thursday as its first day (January 1st), or a year year in the proleptic Gregorian calendar that has a Wednesday as its first day (January 1st) and where year is a number divisible by 400, or a number divisible by 4 but not by 100. All other week-years have 52 weeks.
The week number of the last day of a week-year with 53 weeks is 53; the week number of the last day of a week-year with 52 weeks is 52.
The week-year number of a particular day can be different than the number of the year that contains that day in the proleptic Gregorian calendar. The first week in a week-year y is the week that contains the first Thursday of the Gregorian year y.
For modern purposes, a week as defined here is equivalent to ISO weeks as defined in ISO 8601. [ISO8601]
A string is a valid week string representing a week-year year and week week if it consists of the following components in the given order:
-
Four or more ASCII digits, representing year, where year > 0
-
A U+002D HYPHEN-MINUS character (-)
-
A U+0057 LATIN CAPITAL LETTER W character (W)
-
Two ASCII digits, representing the week week, in the range 1 ≤ week ≤ maxweek, where maxweek is the week number of the last day of week-year year
The rules to parse a week string are as follows. This will return either a week-year number and week number, or nothing. If at any point the algorithm says that it "fails", this means that it is aborted at that point and returns nothing.
-
Let input be the string being parsed.
-
Let position be a pointer into input, initially pointing at the start of the string.
-
Collect a sequence of characters that are ASCII digits. If the collected sequence is not at least four characters long, then fail. Otherwise, interpret the resulting sequence as a base-ten integer. Let that number be the year.
-
If year is not a number greater than zero, then fail.
-
If position is beyond the end of input or if the character at position is not a U+002D HYPHEN-MINUS character, then fail. Otherwise, move position forwards one character.
-
If position is beyond the end of input or if the character at position is not a U+0057 LATIN CAPITAL LETTER W character (W), then fail. Otherwise, move position forwards one character.
-
Collect a sequence of characters that are ASCII digits. If the collected sequence is not exactly two characters long, then fail. Otherwise, interpret the resulting sequence as a base-ten integer. Let that number be the week.
-
Let maxweek be the week number of the last day of year year.
-
If week is not a number in the range 1 ≤ week ≤ maxweek, then fail.
-
If position is not beyond the end of input, then fail.
-
Return the week-year number year and the week number week.
2.4.5.9. Durations
A duration consists of a number of seconds.
Since months and seconds are not comparable (a month is not a precise number of seconds, but is instead a period whose exact length depends on the precise day from which it is measured) a duration as defined in this specification cannot include months (or years, which are equivalent to twelve months). Only durations that describe a specific number of seconds can be described.
A string is a valid duration string representing a duration t if it consists of either of the following:
-
A literal U+0050 LATIN CAPITAL LETTER P character followed by one or more of the following subcomponents, in the order given, where the number of days, hours, minutes, and seconds corresponds to the same number of seconds as in t:
-
One or more ASCII digits followed by a U+0044 LATIN CAPITAL LETTER D character, representing a number of days.
-
A U+0054 LATIN CAPITAL LETTER T character followed by one or more of the following subcomponents, in the order given:
-
One or more ASCII digits followed by a U+0048 LATIN CAPITAL LETTER H character, representing a number of hours.
-
One or more ASCII digits followed by a U+004D LATIN CAPITAL LETTER M character, representing a number of minutes.
-
The following components:
-
One or more ASCII digits, representing a number of seconds.
-
Optionally, a U+002E FULL STOP character (.) followed by one, two, or three ASCII digits, representing a fraction of a second.
-
A U+0053 LATIN CAPITAL LETTER S character.
-
-
This, as with a number of other date- and time-related microsyntaxes defined in this specification, is based on one of the formats defined in ISO 8601. [ISO8601]
-
-
One or more duration time components, each with a different duration time component scale, in any order; the sum of the represented seconds being equal to the number of seconds in t.
A duration time component is a string consisting of the following components:
-
Zero or more space characters.
-
One or more ASCII digits, representing a number of time units, scaled by the duration time component scale specified (see below) to represent a number of seconds.
-
If the duration time component scale specified is 1 (i.e., the units are seconds), then, optionally, a U+002E FULL STOP character (.) followed by one, two, or three ASCII digits, representing a fraction of a second.
-
Zero or more space characters.
-
One of the following characters, representing the duration time component scale of the time unit used in the numeric part of the duration time component:
- U+0057 LATIN CAPITAL LETTER W character
- U+0077 LATIN SMALL LETTER W character
-
Weeks. The scale is 604800.
- U+0044 LATIN CAPITAL LETTER D character
- U+0064 LATIN SMALL LETTER D character
-
Days. The scale is 86400.
- U+0048 LATIN CAPITAL LETTER H character
- U+0068 LATIN SMALL LETTER H character
-
Hours. The scale is 3600.
- U+004D LATIN CAPITAL LETTER M character
- U+006D LATIN SMALL LETTER M character
-
Minutes. The scale is 60.
- U+0053 LATIN CAPITAL LETTER S character
- U+0073 LATIN SMALL LETTER S character
-
Seconds. The scale is 1.
-
Zero or more space characters.
This is not based on any of the formats in ISO 8601. It is intended to be a more human-readable alternative to the ISO 8601 duration format.
-
The rules to parse a duration string are as follows. This will return either a duration or nothing. If at any point the algorithm says that it "fails", this means that it is aborted at that point and returns nothing.
-
Let input be the string being parsed.
-
Let position be a pointer into input, initially pointing at the start of the string.
-
Let months, seconds, and component count all be zero.
-
Let M-disambiguator be minutes.
This flag’s other value is months. It is used to disambiguate the "M" unit in ISO8601 durations, which use the same unit for months and minutes. Months are not allowed, but are parsed for future compatibility and to avoid misinterpreting ISO8601 durations that would be valid in other contexts.
-
If position is past the end of input, then fail.
-
If the character in input pointed to by position is a U+0050 LATIN CAPITAL LETTER P character, then advance position to the next character, set M-disambiguator to months, and skip white space.
-
Run the following substeps in a loop, until a step requiring the loop to be broken or the entire algorithm to fail is reached:
-
Let units be undefined. It will be assigned one of the following values: years, months, weeks, days, hours, minutes, and seconds.
-
Let next character be undefined. It is used to process characters from the input.
-
If position is past the end of input, then break the loop.
-
If the character in input pointed to by position is a U+0054 LATIN CAPITAL LETTER T character, then advance position to the next character, set M-disambiguator to minutes, skip white space, and return to the top of the loop.
-
Set next character to the character in input pointed to by position.
-
If next character is a U+002E FULL STOP character (.), then let N equal zero. (Do not advance position. That is taken care of below.)
Otherwise, if next character is an ASCII digit, then collect a sequence of characters that are ASCII digits, interpret the resulting sequence as a base-ten integer, and let N be that number.
Otherwise next character is not part of a number; fail.
-
If position is past the end of input, then fail.
-
Set next character to the character in input pointed to by position, and this time advance position to the next character. (If next character was a U+002E FULL STOP character (.) before, it will still be that character this time.)
-
If next character is a U+002E FULL STOP character (.), then run these substeps:
-
Collect a sequence of characters that are ASCII digits. Let s be the resulting sequence.
-
If s is the empty string, then fail.
-
Let length be the number of characters in s.
-
Let fraction be the result of interpreting s as a base-ten integer, and then dividing that number by 10length.
-
Increment N by fraction.
-
If position is past the end of input, then fail.
-
Set next character to the character in input pointed to by position, and advance position to the next character.
-
If next character is neither a U+0053 LATIN CAPITAL LETTER S character nor a U+0073 LATIN SMALL LETTER S character, then fail.
-
Set units to seconds.
Otherwise, run these substeps:
-
If next character is a space character, then skip white space, set next character to the character in input pointed to by position, and advance position to the next character.
-
If next character is a U+0059 LATIN CAPITAL LETTER Y character, or a U+0079 LATIN SMALL LETTER Y character, set units to years and set M-disambiguator to months.
If next character is a U+004D LATIN CAPITAL LETTER M character or a U+006D LATIN SMALL LETTER M character, and M-disambiguator is months, then set units to months.
If next character is a U+0057 LATIN CAPITAL LETTER W character or a U+0077 LATIN SMALL LETTER W character, set units to weeks and set M-disambiguator to minutes.
If next character is a U+0044 LATIN CAPITAL LETTER D character or a U+0064 LATIN SMALL LETTER D character, set units to days and set M-disambiguator to minutes.
If next character is a U+0048 LATIN CAPITAL LETTER H character or a U+0068 LATIN SMALL LETTER H character, set units to hours and set M-disambiguator to minutes.
If next character is a U+004D LATIN CAPITAL LETTER M character or a U+006D LATIN SMALL LETTER M character, and M-disambiguator is minutes, then set units to minutes.
If next character is a U+0053 LATIN CAPITAL LETTER S character or a U+0073 LATIN SMALL LETTER S character, set units to seconds and set M-disambiguator to minutes.
Otherwise if next character is none of the above characters, then fail.
-
-
Increment component count.
-
Let multiplier be 1.
-
If units is years, multiply multiplier by 12 and set units to months.
-
If units is months, add the product of N and multiplier to months.
Otherwise, run these substeps:
-
If units is weeks, multiply multiplier by 7 and set units to days.
-
If units is days, multiply multiplier by 24 and set units to hours.
-
If units is hours, multiply multiplier by 60 and set units to minutes.
-
If units is minutes, multiply multiplier by 60 and set units to seconds.
-
Forcibly, units is now seconds. Add the product of N and multiplier to seconds.
-
-
-
If component count is zero, fail.
-
If months is not zero, fail.
-
Return the duration consisting of seconds seconds.
2.4.5.10. Vaguer moments in time
A string is a valid date string with optional time if it is also one of the following:
The rules to parse a date or time string are as follows. The algorithm will return either a date, a time, a global date and time, or nothing. If at any point the algorithm says that it "fails", this means that it is aborted at that point and returns nothing.
-
Let input be the string being parsed.
-
Let position be a pointer into input, initially pointing at the start of the string.
-
Set start position to the same position as position.
-
Set the date present and time present flags to true.
-
Parse a date component to obtain year, month, and day. If this fails, then set the date present flag to false.
-
If date present is true, and position is not beyond the end of input, and the character at position is either a U+0054 LATIN CAPITAL LETTER T character (T) or a U+0020 SPACE character, then advance position to the next character in input.
Otherwise, if date present is true, and either position is beyond the end of input or the character at position is neither a U+0054 LATIN CAPITAL LETTER T character (T) nor a U+0020 SPACE character, then set time present to false.
Otherwise, if date present is false, set position back to the same position as start position.
-
If the time present flag is true, then parse a time component to obtain hour, minute, and second. If this returns nothing, then fail.
-
If the date present and time present flags are both true, but position is beyond the end of input, then fail.
-
If the date present and time present flags are both true, parse a time-zone offset component to obtain timezonehours and timezoneminutes. If this returns nothing, then fail.
-
If position is not beyond the end of input, then fail.
-
If the date present flag is true and the time present flag is false, then let date be the date with year year, month month, and day day, and return date.
Otherwise, if the time present flag is true and the date present flag is false, then let time be the time with hour hour, minute minute, and second second, and return time.
Otherwise, let time be the moment in time at year year, month month, day day, hours hour, minute minute, second second, subtracting timezonehours hours and timezoneminutes minutes, that moment in time being a moment in the UTC time zone; let timezone be timezonehours hours and timezoneminutes minutes from UTC; and return time and timezone.
2.4.6. Colors
A simple color consists of three 8-bit numbers in the range 0..255, representing the red, green, and blue components of the color respectively, in the sRGB color space. [SRGB]
A string is a valid simple color if it is exactly seven characters long, and the first character is a U+0023 NUMBER SIGN character (#), and the remaining six characters are all ASCII hex digits, with the first two digits representing the red component, the middle two digits representing the green component, and the last two digits representing the blue component, in hexadecimal.
A string is a valid lowercase simple color if it is a valid simple color and doesn’t use any characters in the range U+0041 LATIN CAPITAL LETTER A to U+0046 LATIN CAPITAL LETTER F.
The rules for parsing simple color values are as given in the following algorithm. When invoked, the steps must be followed in the order given, aborting at the first step that returns a value. This algorithm will return either a simple color or an error.
-
Let input be the string being parsed.
-
If input is not exactly seven characters long, then return an error.
-
If the first character in input is not a U+0023 NUMBER SIGN character (#), then return an error.
-
If the last six characters of input are not all ASCII hex digits, then return an error.
-
Let result be a simple color.
-
Interpret the second and third characters as a hexadecimal number and let the result be the red component of result.
-
Interpret the fourth and fifth characters as a hexadecimal number and let the result be the green component of result.
-
Interpret the sixth and seventh characters as a hexadecimal number and let the result be the blue component of result.
-
Return result.
The rules for serializing simple color values given a simple color are as given in the following algorithm:
-
Let result be a string consisting of a single U+0023 NUMBER SIGN character (#).
-
Convert the red, green, and blue components in turn to two-digit hexadecimal numbers using lowercase ASCII hex digits, zero-padding if necessary, and append these numbers to result, in the order red, green, blue.
-
Return result, which will be a valid lowercase simple color.
Some obsolete legacy attributes parse colors in a more complicated manner, using the rules for parsing a legacy color value, which are given in the following algorithm. When invoked, the steps must be followed in the order given, aborting at the first step that returns a value. This algorithm will return either a simple color or an error.
-
Let input be the string being parsed.
-
If input is the empty string, then return an error.
-
Strip leading and trailing white space from input.
-
If input is an ASCII case-insensitive match for the string "
transparent
", then return an error. -
If input is an ASCII case-insensitive match for one of the named colors, then return the simple color corresponding to that keyword. [CSS3COLOR]
CSS2 System Colors are not recognized.
-
If input is four characters long, and the first character in input is a U+0023 NUMBER SIGN character (#), and the last three characters of input are all ASCII hex digits, then run these substeps:
-
Let result be a simple color.
-
Interpret the second character of input as a hexadecimal digit; let the red component of result be the resulting number multiplied by 17.
-
Interpret the third character of input as a hexadecimal digit; let the green component of result be the resulting number multiplied by 17.
-
Interpret the fourth character of input as a hexadecimal digit; let the blue component of result be the resulting number multiplied by 17.
-
Return result.
-
-
Replace any characters in input that have a Unicode code point greater than U+FFFF (i.e., any characters that are not in the basic multilingual plane) with the two-character string "
00
". -
If input is longer than 128 characters, truncate input, leaving only the first 128 characters.
-
If the first character in input is a U+0023 NUMBER SIGN character (#), remove it.
-
Replace any character in input that is not an ASCII hex digit with the character U+0030 DIGIT ZERO (0).
-
While input’s length is zero or not a multiple of three, append a U+0030 DIGIT ZERO (0) character to input.
-
Split input into three strings of equal length, to obtain three components. Let length be the length of those components (one third the length of input).
-
If length is greater than 8, then remove the leading length-8 characters in each component, and let length be 8.
-
While length is greater than two and the first character in each component is a U+0030 DIGIT ZERO (0) character, remove that character and reduce length by one.
-
If length is still greater than two, truncate each component, leaving only the first two characters in each.
-
Let result be a simple color.
-
Interpret the first component as a hexadecimal number; let the red component of result be the resulting number.
-
Interpret the second component as a hexadecimal number; let the green component of result be the resulting number.
-
Interpret the third component as a hexadecimal number; let the blue component of result be the resulting number.
-
Return result.
2.4.7. Space-separated tokens
A set of space-separated tokens is a string containing zero or more words (known as tokens) separated by one or more space characters, where words consist of any string of one or more characters, none of which are space characters.
A string containing a set of space-separated tokens may have leading or trailing space characters.
An unordered set of unique space-separated tokens is a set of space-separated tokens where none of the tokens are duplicated.
An ordered set of unique space-separated tokens is a set of space-separated tokens where none of the tokens are duplicated but where the order of the tokens is meaningful.
Sets of space-separated tokens sometimes have a defined set of allowed values. When a set of allowed values is defined, the tokens must all be from that list of allowed values; other values are non-conforming. If no such set of allowed values is provided, then all values are conforming.
How tokens in a set of space-separated tokens are to be compared (e.g., case-sensitively or not) is defined on a per-set basis.
When a user agent has to split a string on spaces, it must use the following algorithm:
-
Let input be the string being parsed.
-
Let position be a pointer into input, initially pointing at the start of the string.
-
Let tokens be an ordered list of tokens, initially empty.
-
While position is not past the end of input:
-
Collect a sequence of characters that are not space characters.
-
Append the string collected in the previous step to tokens.
-
-
Return tokens.
2.4.8. Comma-separated tokens
A set of comma-separated tokens is a string containing zero or more tokens each separated from the next by a single U+002C COMMA character (,), where tokens consist of any string of zero or more characters, neither beginning nor ending with space characters, nor containing any U+002C COMMA characters (,), and optionally surrounded by space characters.
For instance, the string " a ,b, ,d d
" consists of four tokens:
"a", "b", the empty string, and "d d". Leading and trailing white space around each token
doesn’t count as part of the token, and the empty string can be a token.
Sets of comma-separated tokens sometimes have further restrictions on what consists a valid token. When such restrictions are defined, the tokens must all fit within those restrictions; other values are non-conforming. If no such restrictions are specified, then all values are conforming.
When a user agent has to split a string on commas, it must use the following algorithm:
-
Let input be the string being parsed.
-
Let position be a pointer into input, initially pointing at the start of the string.
-
Let tokens be an ordered list of tokens, initially empty.
-
Token: If position is past the end of input, jump to the last step.
-
Collect a sequence of characters that are not U+002C COMMA characters (,). Let s be the resulting sequence (which might be the empty string).
-
Append s to tokens.
-
If position is not past the end of input, then the character at position is a U+002C COMMA character (,); advance position past that character.
-
Jump back to the step labeled token.
-
Return tokens.
2.4.9. References
A valid hash-name reference to an element of type type is a
string consisting of a U+0023 NUMBER SIGN character (#) followed by a string which exactly matches
the value of the name
attribute of an element with type type in
the document.
The rules for parsing a hash-name reference to an element of type type, given a context node scope, are as follows:
-
If the string being parsed does not contain a U+0023 NUMBER SIGN character, or if the first such character in the string is the last character in the string, then return null and abort these steps.
-
Let s be the string from the character immediately after the first U+0023 NUMBER SIGN character in the string being parsed up to the end of that string.
-
Return the first element of type type in tree order in the subtree rooted at scope that has an
id
attribute whose value is a case-sensitive match for s or aname
attribute whose value is a compatibility caseless match for s.
2.4.10. Media queries
A string is a valid media query list if it matches the <media-query-list>
production of the Media Queries specification. [MEDIAQ]
A string matches the environment of the user if it is the empty string, a string consisting of only space characters, or is a media query list that matches the user’s environment according to the definitions given in the Media Queries specification. [MEDIAQ]
2.5. URLs
2.5.1. Terminology
A URL is a valid URL if it conforms to the authoring conformance requirements in the WHATWG URL specification. [URL]
A string is a valid non-empty URL if it is a valid URL but it is not the empty string.
A string is a valid URL potentially surrounded by spaces if, after stripping leading and trailing white space from it, it is a valid URL.
A string is a valid non-empty URL potentially surrounded by spaces if, after stripping leading and trailing white space from it, it is a valid non-empty URL.
This specification defines the URL about:legacy-compat
as a reserved,
though unresolvable, about:
URL, for use in DOCTYPEs in HTML documents when needed for compatibility with XML tools. [RFC6694]
This specification defines the URL about:html-kind
as a reserved,
though unresolvable, about:
URL, that is used as an
identifier for kinds of media tracks. [RFC6694]
This specification defines the URL about:srcdoc
as a reserved, though
unresolvable, about:
URL, that is used as the document’s URL of iframe
srcdoc
documents. [RFC6694]
The fallback base URL of a Document
object is the absolute URL obtained by running these substeps:
-
If document is an
iframe
srcdoc
document, then return the document base URL of the Document’s browsing context’s browsing context container’s node document. -
If document’s URL is
about:blank
, and the Document’s browsing context has a creator browsing context, then return the creator base URL. -
Return document’s URL.
The document base URL of a Document
object is the absolute URL obtained by running these substeps:
-
If there is no
base
element that has anhref
attribute in theDocument
, then the document base URL is theDocument
's fallback base URL; abort these steps. -
Otherwise, the document base URL is the frozen base URL of the first
base
element in theDocument
that has anhref
attribute, in tree order.
2.5.2. Parsing URLs
Parsing a URL is the process of taking a URL string and obtaining the URL record that it implies. While this process is defined in the WHATWG URL specification, this specification defines a wrapper for convenience. [URL]
This wrapper is only useful when the character encoding for the URL parser has to match that of the document or environment settings object for legacy reasons. When that is not the case the URL parser can be used directly.
To parse a URL url, relative to either a document or environment settings object, the user agent must use the following steps. Parsing a URL either results in failure or a resulting URL string and resulting URL record.
-
Let encoding be document’s character encoding, if document was given, and environment settings object’s API URL character encoding otherwise.
-
Let baseURL be document’s base URL, if document was given, and environment settings object’s API base URL otherwise.
-
Let urlRecord be the result of applying the URL parser to url, with baseURL and encoding.
-
If urlRecord is failure, then abort these steps with an error.
-
Let urlString be the result of applying the URL serializer to urlRecord.
-
Return urlString as the resulting URL string and urlRecord as the resulting URL record.
2.5.3. Dynamic changes to base URLs
When a document’s document base URL changes, all elements in that document are affected by a base URL change.
The following are base URL change steps, which run when an element is affected by a base URL change (as defined by the DOM specification):
- If the element creates a hyperlink
-
If the URL identified by the hyperlink is being shown to the user, or if any
data derived from that URL is affecting the display, then the
href
attribute should be reparsed relative to the element’s node document and the UI updated appropriately.For example, the CSS :link/:visited pseudo-classes might have been affected.
- If the element is a
q
,blockquote
,ins
, ordel
element with acite
attribute - If the URL identified by the
cite
attribute is being shown to the user, or if any data derived from that URL is affecting the display, then the URL should be reparsed relative to the element’s node document and the UI updated appropriately. - Otherwise
-
The element is not directly affected.
For instance, changing the base URL doesn’t affect the image displayed by
img
elements, although subsequent accesses of thesrc
IDL attribute from script will return a new absolute URL that might no longer correspond to the image being shown.
2.6. Fetching resources
2.6.1. Terminology
User agents can implement a variety of transfer protocols, but this specification mostly defines behavior in terms of HTTP. [HTTP]
The HTTP GET method is equivalent to the default retrieval action of the protocol. For example, RETR in FTP. Such actions are idempotent and safe, in HTTP terms.
The HTTP response codes are equivalent to statuses in other protocols that have the same basic meanings. For example, a "file not found" error is equivalent to a 404 code, a server error is equivalent to a 5xx code, and so on.
The HTTP headers are equivalent to fields in other protocols that have the same basic meaning. For example, the HTTP authentication headers are equivalent to the authentication aspects of the FTP protocol.
A referrer source is either a Document
or a URL.
To create a potential-CORS request, given a url, corsAttributeState, and an optional same-origin fallback flag, run these steps:
-
Let mode be "
no-cors
" if corsAttributeState is No CORS, and "cors
" otherwise. -
If same-origin fallback flag is set and mode is "
no-cors
", set mode to "same-origin
". -
Let credentialsMode be "
include
". -
If corsAttributeState is Anonymous, set credentialsMode to "
same-origin
". -
Let request be a new request whose URL is url, destination is "
subresource
", mode is mode, credentials mode is credentialsMode, and whose use-URL-credentials flag is set.
2.6.2. Processing model
When a user agent is to fetch a resource or URL, optionally from an origin origin, optionally using a specific referrer source as an override referrer source, and optionally with any of a synchronous flag, a manual redirect flag, a force same-origin flag, and a block cookies flag, the following steps must be run. (When a URL is to be fetched, the URL identifies a resource to be obtained.)
-
If there is a specific override referrer source, and it is a URL, then let referrer be the override referrer source, and jump to the step labeled clean referrer.
-
Let document be the appropriate
Document
as given by the following list:- If there is a specific override referrer source
- The override referrer source.
- When navigating
- The active document of the source browsing context.
- When fetching resources for an element
- The element’s
Document
.
-
While document is an
iframe
srcdoc
document, let document be document’s browsing context’s browsing context container’sDocument
instead. -
If the origin of Document is not a scheme/host/port tuple, then set referrer to the empty string and jump to the step labeled Clean referrer.
-
Let referrer be document’s URL.
-
Clean referrer: Apply the URL parser to referrer and let parsed referrer be the resulting URL record.
-
Let referrer be the result of applying the URL serializer to parsed referrer, with the exclude fragment flag set.
-
If referrer is not the empty string, is not a
data:
URL, and is not the URL "about:blank
", then generate the address of the resource from which Request-URIs are obtained as required by HTTP for theReferer
(sic) header from referrer. [HTTP]Otherwise, the
Referer
(sic) header must be omitted, regardless of its value. -
If the algorithm was not invoked with the synchronous flag, perform the remaining steps in parallel.
-
If the
Document
with which any tasks queued by this algorithm would be associated doesn’t have an associated browsing context, then abort these steps. -
This is the main step.
If the resource is identified by an absolute URL, and the resource is to be obtained using an idempotent action (such as an HTTP GET or equivalent), and it is already being downloaded for other reasons (e.g., another invocation of this algorithm), and this request would be identical to the previous one (e.g., same
Accept
andOrigin
headers), and the user agent is configured such that it is to reuse the data from the existing download instead of initiating a new one, then use the results of the existing download instead of starting a new one.Otherwise, if the resource is identified by an absolute URL with a scheme that does not define a mechanism to obtain the resource (e.g., it is a
mailto:
URL) or that the user agent does not support, then act as if the resource was an HTTP 204 No Content response with no other metadata.Otherwise, if the resource is identified by the URL
about:blank
, then the resource is immediately available and consists of the empty string, with no metadata.Otherwise, at a time convenient to the user and the user agent, download (or otherwise obtain) the resource, applying the semantics of the relevant specifications (e.g., performing an HTTP GET or POST operation, or reading the file from disk, or expanding
data:
URLs, etc).For the purposes of the
Referer
(sic) header, use the address of the resource from which Request-URIs are obtained generated in the earlier step.For the purposes of the
Origin
header, if the fetching algorithm was explicitly initiated from an origin, then the origin that initiated the HTTP request is origin. Otherwise, this is a request from a "privacy-sensitive" context. [ORIGIN] -
If the algorithm was not invoked with the block cookies flag, and there are cookies to be set, update the cookies. [COOKIES]
-
If the fetched resource is an HTTP redirect or equivalent, then:
- If the force same-origin flag is set and the URL of the target of the redirect does not have the same origin as the URL for which the fetch algorithm was invoked
- Abort these steps and return failure from this algorithm, as if the remote host could not be contacted.
- If the manual redirect flag is set
- Continue, using the fetched resource (the redirect) as the result of the algorithm. If the calling algorithm subsequently requires the user agent to transparently follow the redirect, then the user agent must resume this algorithm from the main step, but using the target of the redirect as the resource to fetch, rather than the original resource.
- Otherwise
-
First, apply any relevant requirements for redirects (such as showing any appropriate
prompts). Then, redo main step, but using the target of the redirect as the
resource to fetch, rather than the original resource. For HTTP requests, the new request
must include the same headers as the original request, except for headers for which
other requirements are specified (such as the
Host
header). [HTTP]The HTTP specification requires that 301, 302, and 307 redirects, when applied to methods other than the safe methods, not be followed without user confirmation. That would be an appropriate prompt for the purposes of the requirement in the paragraph above. [HTTP]
-
If the algorithm was not invoked with the synchronous flag: When the resource is available, or if there is an error of some description, queue a task that uses the resource as appropriate. If the resource can be processed incrementally, as, for instance, with a progressively interlaced JPEG or an HTML file, additional tasks may be queued to process the data as it is downloaded. The task source for these tasks is the networking task source.
Otherwise, return the resource or error information to the calling algorithm.
If the user agent can determine the actual length of the resource being fetched for an
instance of this algorithm, and if that length is finite, then that length is the file’s size. Otherwise, the subject of the algorithm (that is, the resource being fetched)
has no known size. (For example, the HTTP Content-Length
header might
provide this information.)
The user agent must also keep track of the number of bytes downloaded for each instance of this algorithm. This number must exclude any out-of-band metadata, such as HTTP headers.
The navigation processing model handles redirects itself, overriding the redirection handling that would be done by the fetching algorithm.
Whether the type sniffing rules apply to the fetched resource depends on the algorithm that invokes the rules — they are not always applicable.
2.6.3. Encrypted HTTP and related security concerns
Anything in this specification that refers to HTTP also applies to HTTP-over-TLS, as represented
by URLs representing the https
scheme. [HTTP]
User agents should report certificate errors to the user and must either refuse to download resources sent with erroneous certificates or must act as if such resources were in fact served with no encryption.
User agents should warn the user that there is a potential problem whenever the user visits a page that the user has previously visited, if the page uses less secure encryption on the second visit.
Not doing so can result in users not noticing man-in-the-middle attacks.
If a user connects to a server with full encryption, but the page then refers to an external resource that has an expired certificate, then the user agent will act as if the resource was unavailable, possibly also reporting the problem to the user. If the user agent instead allowed the resource to be used, then an attacker could just look for "secure" sites that used resources from a different host and only apply man-in-the-middle attacks to that host, for example taking over scripts in the page.
If a user bookmarks a site that uses a CA-signed certificate, and then later revisits that site directly but the site has started using a self-signed certificate, the user agent could warn the user that a man-in-the-middle attack is likely underway, instead of simply acting as if the page was not encrypted.
2.6.4. Determining the type of a resource
The Content-Type metadata of a resource must be obtained and interpreted in a manner consistent with the requirements of the MIME Sniffing specification. [MIMESNIFF]
The computed type of a resource must be found in a manner consistent with the requirements given in the MIME Sniffing specification for finding the computed media type of the relevant sequence of octets. [MIMESNIFF]
The rules for sniffing images specifically and the rules for distinguishing if a resource is text or binary are also defined in the MIME Sniffing specification. Both sets of rules return a MIME type as their result. [MIMESNIFF]
It is imperative that the rules in the MIME Sniffing specification be followed exactly. When a user agent uses different heuristics for content type detection than the server expects, security problems can occur. For more details, see the MIME Sniffing specification. [MIMESNIFF]
2.6.5. Extracting character encodings from meta
elements
The algorithm for extracting a character encoding from a meta
element,
given a string s, is as follows. It either returns a character encoding or nothing.
-
Let position be a pointer into s, initially pointing at the start of the string.
-
Loop: Find the first seven characters in s after position that are an ASCII case-insensitive match for the word "
charset
". If no such match is found, return nothing and abort these steps. -
Skip any space characters that immediately follow the word "
charset
" (there might not be any). -
If the next character is not a U+003D EQUALS SIGN (=), then move position to point just before that next character, and jump back to the step labeled loop.
-
Skip any space characters that immediately follow the equals sign (there might not be any).
-
Process the next character as follows:
- If it is a U+0022 QUOTATION MARK character (") and there is a later U+0022 QUOTATION MARK character (") in s
- If it is a U+0027 APOSTROPHE character (') and there is a later U+0027 APOSTROPHE character (') in s
- Return the result of getting an encoding from the substring that is between this character and the next earliest occurrence of this character.
- If it is an unmatched U+0022 QUOTATION MARK character (")
- If it is an unmatched U+0027 APOSTROPHE character (')
- If there is no next character
- Return nothing.
- Otherwise
- Return the result of getting an encoding from the substring that consists of this character up to but not including the first space character or U+003B SEMICOLON character (;), or the end of s, whichever comes first.
This algorithm is distinct from those in the HTTP specification (for example, HTTP doesn’t allow the use of single quotes and requires supporting a backslash-escape mechanism that is not supported by this algorithm). While the algorithm is used in contexts that, historically, were related to HTTP, the syntax as supported by implementations diverged some time ago. [HTTP]
2.6.6. CORS settings attributes
A CORS settings attribute is an enumerated attribute. The following table lists the keywords and states for the attribute — the keywords in the left column map to the states in the cell in the second column on the same row as the keyword.
Keyword | State | Brief description |
---|---|---|
anonymous
| Anonymous | Requests for the element will have their mode set to "cors " and
their credentials mode set to "same-origin ".
|
use-credentials
| Use Credentials | Requests for the element will have their mode set to "cors " and
their credentials mode set to "include ".
|
The empty string is also a valid keyword, and maps to the Anonymous state. The attribute’s invalid value default is the Anonymous state. For the purposes of reflection,
the canonical case for the Anonymous state is the anonymous
keyword. The missing value default, used when the attribute is omitted, is the No CORS state.
2.6.7. Referrer policy attributes
A referrer policy attribute is an enumerated attribute. Each referrer policy, including the empty string, is a keyword for this attribute, mapping to a state of the same name.
The attribute’s invalid value default and missing value default are both the empty string state.
The impact of these states on the processing model of various fetches is defined in more detail throughout this specification, in the WHATWG Fetch standard, and in Referrer Policy. [FETCH] [REFERRERPOLICY]
- First, the presence of a <{link/}noreferrer}> link type;
- Then, the value of a referrer policy attribute;
- Then, the presence of any
meta
element withname
attribute set toreferrer
. - Finally, the
HTTP header.Referrer-Policy
2.7. Common DOM interfaces
2.7.1. Reflecting content attributes in IDL attributes
Some IDL attributes are defined to reflect a particular content attribute. This means that on getting, the IDL attribute returns the current value of the content attribute, and on setting, the IDL attribute changes the value of the content attribute to the given value.
In general, on getting, if the content attribute is not present, the IDL attribute must act as if the content attribute’s value is the empty string; and on setting, if the content attribute is not present, it must first be added.
If a reflecting IDL attribute is a USVString
attribute whose content attribute
is defined to contain a URLs, then on getting, if the content attribute is
absent, the IDL attribute must return the empty string. Otherwise, the IDL attribute must parse the value of the content attribute relative to the element’s node document and
if that is successful, return the resulting URL string. If parsing fails, then the value of
the content attribute must be returned instead, converted to a USVString
. On setting, the content attribute must be set to the specified new
value.
If a reflecting IDL attribute is a DOMString
attribute whose content attribute is
an enumerated attribute, and the IDL attribute is limited to only known values,
then, on getting, the IDL attribute must return the conforming value associated with the state
the attribute is in (in its canonical case), if any, or the empty string if the attribute is in
a state that has no associated keyword value or if the attribute is not in a defined state (e.g.,
the attribute is missing and there is no missing value default); and on setting, the
content attribute must be set to the specified new value.
If a reflecting IDL attribute is a nullable DOMString
attribute whose content
attribute is an enumerated attribute, then, on getting, if the corresponding content
attribute is in its missing value default then the IDL attribute must return null,
otherwise, the IDL attribute must return the conforming value associated with the state the
attribute is in (in its canonical case); and on setting, if the new value is null, the content
attribute must be removed, and otherwise, the content attribute must be set to the specified new
value.
If a reflecting IDL attribute is a DOMString
or USVString
attribute but doesn’t fall into any of the above categories, then the getting and setting must be
done in a transparent, case-preserving manner.
If a reflecting IDL attribute is a boolean
attribute, then on getting the IDL
attribute must return true if the content attribute is set, and false if it is absent. On
setting, the content attribute must be removed if the IDL attribute is set to false, and must be
set to the empty string if the IDL attribute is set to true. (This corresponds to the rules for boolean content attributes.)
If a reflecting IDL attribute has a signed integer type (long
) then, on getting,
the content attribute must be parsed according to the rules for parsing signed integers,
and if that is successful, and the value is in the range of the IDL attribute’s type, the
resulting value must be returned. If, on the other hand, it fails or returns an out of range
value, or if the attribute is absent, then the default value must be returned instead, or 0 if
there is no default value. On setting, the given value must be converted to the shortest
possible string representing the number as a valid integer and then that string must be
used as the new content attribute value.
If a reflecting IDL attribute has a signed integer type (long
)
that is limited to only non-negative numbers then, on getting,
the content attribute
must be parsed according to the rules for parsing non-negative integers, and if that
is successful, and the value is in the range of the IDL attribute’s type, the resulting value
must be returned. If, on the other hand, it fails or returns an out of range value, or if the
attribute is absent, the default value must be returned instead, or -1 if there is no
default value. On setting, if the value is negative, the user agent must throw an IndexSizeError
exception. Otherwise, the given value must be converted to the
shortest possible string representing the number as a valid non-negative integer and then
that string must be used as the new content attribute value.
If a reflecting IDL attribute has an unsigned integer type (unsigned long
)
then, on getting, the content attribute must be parsed according to the rules for parsing
non-negative integers, and if that is successful, and the value is in the range 0 to
2147483647 inclusive, the resulting value must be returned. If, on the other hand, it fails or
returns an out of range value, or if the attribute is absent, the default value must be returned
instead, or 0 if there is no default value. On setting, first, if the new value is in the range
0 to 2147483647, then let n be the new value, otherwise let n be the
default value, or 0 if there is no default value; then, n must be converted to the
shortest possible string representing the number as a valid non-negative integer and that
string must be used as the new content attribute value.
If a reflecting IDL attribute has an unsigned integer type (unsigned long
) that is limited to only non-negative numbers greater than zero, then the
behavior is similar
to the previous case, but zero is not allowed. On getting, the content attribute must first be
parsed according to the rules for parsing non-negative integers, and if that is
successful, and the value is in the range 1 to 2147483647 inclusive, the resulting value must be
returned. If, on the other hand, it fails or returns an out of range value, or if the attribute
is absent, the default value must be returned instead, or 1 if there is no default value. On
setting, if the value is zero, the user agent must throw an IndexSizeError
exception. Otherwise, first, if the new value is in the range 1 to 2147483647, then let n be the new value, otherwise let n be the default value, or 1 if there is
no default value; then, n must be converted to the shortest possible string
representing the number as a valid non-negative integer and that string must be used as
the new content attribute value.
If a reflecting IDL attribute has a floating-point number type (double
or unrestricted double
), then, on getting, the content attribute must be parsed
according to the rules for parsing floating-point number values, and if that is
successful, the resulting value must be returned. If, on the other hand, it fails, or if the
attribute is absent, the default value must be returned instead, or 0.0 if there is no default
value. On setting, the given value must be converted to the best representation of the number as a floating-point number and then that string must be used as the new content attribute value.
If a reflecting IDL attribute has a floating-point number type (double
or unrestricted double
) that is limited to numbers greater than zero, then
the behavior is similar to the previous case, but zero and negative values are not allowed. On
getting, the content attribute must be parsed according to the rules for parsing
floating-point number values, and if that is successful and the value is greater than 0.0,
the resulting value must be returned. If, on the other hand, it fails or returns an out of range
value, or if the attribute is absent, the default value must be returned instead, or 0.0 if
there is no default value. On setting, if the value is less than or equal to zero, then the
value must be ignored. Otherwise, the given value must be converted to the best representation of the number as a floating-point number and then that string must be used as the new content attribute value.
The values Infinity and Not-a-Number (NaN) values throw an exception on setting, as defined in the Web IDL specification. [WEBIDL]
If a reflecting IDL attribute has the type DOMTokenList
, then on getting it must return a DOMTokenList
object whose associated element is the element in question and whose associated
attribute’s local name is the name of the attribute in question.
If a reflecting IDL attribute has the type HTMLElement
, or an interface that
descends from HTMLElement
, then, on getting, it must run the following algorithm
(stopping at the first point where a value is returned):
-
If the corresponding content attribute is absent, then the IDL attribute must return null.
-
Let candidate be the element that the
document.getElementById()
method would find when called on the content attribute’s element’s node document if it were passed as its argument the current value of the corresponding content attribute. -
If candidate is null, or if it is not type-compatible with the IDL attribute, then the IDL attribute must return null.
-
Otherwise, it must return candidate.
On setting, if the given element has an id
attribute, and has the same tree as the element of the attribute being set, and the given element is the
first element in that tree whose ID is the value of that id
attribute, then the content attribute must be set to the value of that id
attribute. Otherwise, the content attribute must be set to the empty string.
2.7.2. Collections
The HTMLFormControlsCollection
and HTMLOptionsCollection
interfaces are collections derived from the HTMLCollection
interface. The HTMLAllCollection
however, is independent as it has a variety of unique quirks that are not
desirable to inherit from HTMLCollection
.
2.7.2.1. The HTMLAllCollection
interface
The HTMLAllCollection
interface is used for the legacy document.all
attribute. It operates similarly to HTMLCollection
; it also supports a variety of
other legacy features required for web compatibility such as the ability to be invoked like a
function (legacycaller
).
All HTMLAllCollection
objects are rooted at a Document
and have a filter that
matches all elements, so the elements represented by the collection of an HTMLAllCollection
object consist of all the descendant elements of the root Document
.
[LegacyUnenumerableNamedProperties] interface HTMLAllCollection { readonly attribute unsigned long length; getter Element? (unsigned long index); getter (HTMLCollection or Element)? namedItem(DOMString name); legacycaller (HTMLCollection or Element)? item(optional DOMString nameOrItem); };
- collection .
length
- Returns the number of elements in the collection.
- element = collection .
item
(index) - element = collection(index)
- element = collection[index]
- Returns the item with index index from the collection (determined by tree order.
- element = collection .
item
(name) - collection = collection .
item
(name) - element = collection .
namedItem
(name) - collection = collection .
namedItem
(name) - element = collection(name)
- collection = collection(name)
- element = collection[name]
- collection = collection[name]
-
Returns the item with ID or name name from the collection.
If there are multiple matching items, then an
HTMLCollection
object containing all those elements is returned.The
name
attribute’s value provides a name forbutton
,input
,select
, andtextarea
. Similarly,iframe
'sname
,object
'sname
,meta
'sname
,map
'sname
, andform
'sname
attribute’s value provides a name for their respective elements. Only the elements mentioned have a name for the purpose of this method.
The object’s supported property indices are as defined for HTMLCollection
objects.
The supported property names consist of the non-empty values of all the id
and name attributes of all the elements represented by the collection, in tree order, ignoring later duplicates, with the id
of an element preceding its name if it
contributes both, they differ from each other, and neither is the duplicate of an earlier entry.
On getting, the length
attribute must
return the number of nodes represented by the collection.
The indexed property getter must return the result of getting the "all"-indexed element from this HTMLAllCollection
given the passed index.
The namedItem(name)
method
must return the result of getting the "all"-named element or elements from this HTMLAllCollection
given name.
The item(nameOrIndex)
method
(and the legacycaller
behavior) must act according to the following algorithm:
-
If nameOrIndex was not provided, return null.
-
If nameOrIndex, converted to a JavaScript string value, is an array index property name, return the result of getting the "all"-indexed element from this
HTMLAllCollection
given the number represented by nameOrIndex. -
Return the result of getting the "all"-named element or elements from this
HTMLAllCollection
given nameOrIndex.
The following elements are considered "all"-named elements: a
, applet
, button
, embed
, form
, frame
, frameset
, iframe
, img
, input
, map
, meta
, object
, select
, and textarea
.
To get the "all"-indexed element from an HTMLAllCollection
collection given an index index, return the element
with index index in collection, or null if there is no such element at index.
To get the "all"-named element or elements from an HTMLAllCollection
collection given a name name, run the
following algorithm:
-
If name is the empty string, return null.
-
Let subCollection be an
HTMLCollection
object rooted at the sameDocument
as collection, whose filter matches only elements that are either:-
"all"-named elements with a name attribute equal to name, or,
-
elements with an ID equal to name.
-
-
If there is exactly one element in subCollection, then return that element.
-
Otherwise, if subCollection is empty, return null.
-
Otherwise, return subCollection.
2.7.2.2. The HTMLFormControlsCollection
interface
The HTMLFormControlsCollection
interface is used for collections of listed elements in form
elements.
interface HTMLFormControlsCollection : HTMLCollection { // inherits length and item() getter (RadioNodeList or Element)? namedItem(DOMString name); // shadows inherited namedItem() };
interface RadioNodeList : NodeList { attribute DOMString value; };
- collection .
length
- Returns the number of elements in the collection.
- element = collection .
item
(index) - element = collection[index]
- Returns the item with index index from the collection. The items are sorted in tree order.
- element = collection .
namedItem
(name) - radioNodeList = collection .
namedItem
(name) - element = collection[name]
- radioNodeList = collection[name]
-
Returns the item with ID or
name
name from the collection.If there are multiple matching items, then a
RadioNodeList
object containing all those elements is returned. - radioNodeList .
value
[ = value ] -
Returns the value of the first checked radio button represented by the object.
Can be set, to check the first radio button with the given value represented by the object.
The object’s supported property indices are as defined for HTMLCollection
objects.
The supported property names consist of the non-empty values of all the id
and name
attributes of all the elements represented by the collection, in tree order, ignoring later duplicates, with the id
of an element preceding
its name
if it contributes both, they differ from each other, and neither is the
duplicate of an earlier entry.
The properties exposed in this way must be unenumerable.
The namedItem(name)
method must act according to the
following algorithm:
-
If name is the empty string, return null and stop the algorithm.
-
If, at the time the method is called, there is exactly one node in the collection that has either an
id
attribute or aname
attribute equal to name, then return that node and stop the algorithm. -
Otherwise, if there are no nodes in the collection that have either an
id
attribute or aname
attribute equal to name, then return null and stop the algorithm. -
Otherwise, create a new
RadioNodeList
object representing a live view of theHTMLFormControlsCollection
object, further filtered so that the only nodes in theRadioNodeList
object are those that have either anid
attribute or aname
attribute equal to name. The nodes in theRadioNodeList
object must be sorted in tree order. -
Return that
RadioNodeList
object.
Members of the RadioNodeList
interface inherited from the NodeList
interface must behave as they would on a NodeList
object.
The value
IDL attribute on the RadioNodeList
object, on
getting, must return the value returned by running the following steps:
-
Let element be the first element in tree order represented by the
RadioNodeList
object that is aninput
element whosetype
attribute is in theRadio Button
state and whose checkedness is true. Otherwise, let it be null. -
If element is null, return the empty string.
-
If element is an element with no
value
attribute, return the string "on
". -
Otherwise, return the value of element’s
value
attribute.
On setting, the value
IDL attribute must run the following steps:
-
If the new value is the string "
on
": let element be the first element in tree order represented by theRadioNodeList
object that is aninput
element whosetype
attribute is in theRadio Button
state and whosevalue
content attribute is either absent, or present and equal to the new value, if any. If no such element exists, then instead let element be null.Otherwise: let element be the first element in tree order represented by the
RadioNodeList
object that is aninput
element whosetype
attribute is in theRadio Button
state and whosevalue
content attribute is present and equal to the new value, if any. If no such element exists, then instead let element be null. -
If element is not null, then set its checkedness to true.
2.7.2.3. The HTMLOptionsCollection
interface
The HTMLOptionsCollection
interface is used for collections of option
elements. It is always rooted on a select
element and has
attributes and methods that manipulate that element’s descendants.
interface HTMLOptionsCollection : HTMLCollection { // inherits item(), namedItem() attribute unsigned long length; // shadows inherited length setter void (unsigned long index, HTMLOptionElement? option); void add((HTMLOptionElement or HTMLOptGroupElement) element, optional (HTMLElement or long)? before = null); void remove(long index); attribute long selectedIndex; };
- collection .
length
[ = value ] -
Returns the number of elements in the collection.
When set to a smaller number, truncates the number of
option
elements in the corresponding container.When set to a greater number, adds new blank
option
elements to that container. - element = collection .
item
(index) - element = collection[index]
- Returns the item with index index from the collection. The items are sorted in tree order.
- collection[index] = element
-
When index is a greater number than the number of items in the collection, adds
new blank
option
elements in the corresponding container.When set to null, removes the item at index index from the collection.
When set to an
option
element, adds or replaces it at index index from the collection. - element = collection .
namedItem
(name) - element = collection[name]
-
Returns the item with ID or
name
name from the collection.If there are multiple matching items, then the first is returned.
- collection .
add
(element [, before ] ) -
Inserts element before the node given by before.
The before argument can be a number, in which case element is inserted before the item with that number, or an element from the collection, in which case element is inserted before that element.
If before is omitted, null, or a number out of range, then element will be added at the end of the list.
This method will throw a
HierarchyRequestError
exception if element is an ancestor of the element into which it is to be inserted. - collection .
remove
(index) - Removes the item with index index from the collection.
- collection .
selectedIndex
[ = value ] -
Returns the index of the first selected item, if any, or -1 if there is no selected
item.
Can be set, to change the selection.
The object’s supported property indices are as defined for HTMLCollection
objects.
On getting, the length
attribute
must return the number of nodes represented by the collection.
On setting, the behavior depends on whether the new value is equal to, greater than, or less than
the number of nodes represented by the collection at that time. If the number is the same,
then setting the attribute must do nothing. If the new value is greater, then n new option
elements with no attributes and no child nodes must be appended to the select
element on which the HTMLOptionsCollection
is rooted, where n is the difference between the two numbers (new value minus old value). Mutation
events must be fired as if a DocumentFragment
containing the new option
elements had been inserted. If the new value is lower, then the last n nodes in the
collection must be removed from their parent nodes, where n is the difference between
the two numbers (old value minus new value).
Setting length
never removes or adds any optgroup
elements, and
never adds new children to existing optgroup
elements (though it can remove children from
them).
The supported property names consist of the non-empty values of all the id
and name
attributes of all the elements represented by the collection, in tree order, ignoring later duplicates, with the id
of an element preceding its name
if it contributes both, they differ from each other, and neither is the
duplicate of an earlier entry.
The properties exposed in this way must be unenumerable.
When the user agent is to set the value of a new indexed property or set the value of an existing indexed property for a given property index index to a new value value, it must run the following algorithm:
-
If value is null, invoke the steps for the
remove
method with index as the argument, and abort these steps. -
Let length be the number of nodes represented by the collection.
-
Let n be index minus length.
-
If n is greater than zero, then append a
DocumentFragment
consisting of n-1 newoption
elements with no attributes and no child nodes to theselect
element on which theHTMLOptionsCollection
is rooted. -
If n is greater than or equal to zero, append value to the
select
element. Otherwise, replace the indexth element in the collection by value.
The add(element, before)
method must act according
to the following algorithm:
-
If element is an ancestor of the
select
element on which theHTMLOptionsCollection
is rooted, then throw aHierarchyRequestError
exception and abort these steps. -
If before is an element, but that element isn’t a descendant of the
select
element on which theHTMLOptionsCollection
is rooted, then throw aNotFoundError
exception and abort these steps. -
If element and before are the same element, then return and abort these steps.
-
If before is a node, then let reference be that node. Otherwise, if before is an integer, and there is a beforeth node in the collection, let reference be that node. Otherwise, let reference be null.
-
If reference is not null, let parent be the parent node of reference. Otherwise, let parent be the
select
element on which theHTMLOptionsCollection
is rooted. -
Pre-insert element into parent node before reference.
The remove(index)
method
must act according to the following algorithm:
-
If the number of nodes represented by the collection is zero, abort these steps.
-
If index is not a number greater than or equal to 0 and less than the number of nodes represented by the collection, abort these steps.
-
Let element be the indexth element in the collection.
-
Remove element from its parent node.
The selectedIndex
IDL attribute must
act like the identically named attribute on the select
element on which the HTMLOptionsCollection
is rooted
2.7.3. The DOMStringList
interface
The DOMStringList
interface is a non-fashionable retro way of
representing a list of strings.
interface DOMStringList { readonly attribute unsigned long length; getter DOMString? item(unsigned long index); boolean contains(DOMString string); };
New APIs must use sequence<DOMString>
or equivalent rather than DOMStringList
.
- strings .
length
-
Returns the number of strings in strings.
- strings[index]
- strings .
item()
(index) -
Returns the string with index index from strings.
- strings .
contains()
(string) -
Returns true if strings contains string, and false otherwise.
Each DOMStringList
object has an associated list.
The supported property indices for a DOMStringList
object are the numbers zero to the
associated list’s size minus one. If its associated list is empty, it has no supported property indices.
The length
attribute’s getter must this DOMStringList
object’s associated list’s size.
The item(index)
method,
when invoked, must return the indexth item in this DOMStringList
object’s associated list,
or null if index plus one is less than this DOMStringList
object’s associated list’s size.
The contains(string)
method, when invoked, must return true if this DOMStringList
object’s associated list contains string, and false otherwise.
2.7.4. Garbage collection
There is an implied strong reference from any IDL attribute that returns a pre-existing object to that object.
window.document
attribute on the Window
object means that there is a strong reference
from a Window
object to its Document
object. Similarly, there is
always a strong reference from a Document
to any descendant nodes, and from any
node to its owner node document. 2.8. Namespaces
The HTML namespace is: http://www.w3.org/1999/xhtml
The MathML namespace is: http://www.w3.org/1998/Math/MathML
The SVG namespace is: http://www.w3.org/2000/svg
The XLink namespace is: http://www.w3.org/1999/xlink
The XML namespace is: http://www.w3.org/XML/1998/namespace
The XMLNS namespace is: http://www.w3.org/2000/xmlns/
Data mining tools and other user agents that perform operations on content without running scripts, evaluating CSS or XPath expressions, or otherwise exposing the resulting DOM to arbitrary content, may "support namespaces" by just asserting that their DOM node analogs are in certain namespaces, without actually exposing the above strings.
In the HTML syntax, namespace prefixes and namespace declarations do not have the same effect as in XML. For instance, the colon has no special meaning in HTML element names.
2.9. Safe passing of structured data
This section uses the terminology and typographic conventions from the JavaScript specification. [ECMA-262]
2.9.1. Serializable objects
Serializable objects support being serialized, and later deserialized, in a way
that is independent of any given JavaScript Realm. This allows them to be stored on
disk and later restored, or cloned across Document
and Worker
boundaries (including across
documents of different origins or in different event loops).
Not all objects are serializable objects, and not all aspects of objects that are serializable objects are necessarily preserved when they are serialized.
Platform objects can be serializable objects if they implement only interfaces decorated with the [Serializable]
IDL extended attribute. Such interfaces must also define the following algorithms:
- serialization steps, taking a platform object value, a Record serialized, and a boolean forStorage
-
A set of steps that serializes the data in value into fields of serialized. The resulting data serialized into serialized must be independent of any JavaScript Realm.
These steps may throw an exception if serialization is not possible.
These steps may perform a sub-serialization to serialize nested data structures. They should not call StructuredSerialize directly, as doing so will omit the important memory argument.
The introduction of these steps should omit mention of the forStorage argument if it is not relevant to the algorithm.
- deserialization steps, taking a Record serialized and a platform object value
-
A set of steps that deserializes the data in serialized, using it to set up value as appropriate. value will be a newly-created instance of the platform object type in question, with none of its internal data set up; setting that up is the job of these steps.
These steps may throw an exception if deserialization is not possible.
These steps may perform a sub-deserialization to deserialize nested data structures. They should not call StructuredDeserialize directly, as doing so will omit the important targetRealm and memory arguments.
It is up to the definition of individual platform objects to determine what data is serialized and deserialized by these steps. Typically the steps are very symmetric.
The [Serializable]
extended attribute must take no
arguments, and must not appear on anything other than an interface. It must appear only once on an
interface. It must not be used on a callback interface. If it appears on a partial interface or an
interface that is really a mixin, then it must also appear on the original or mixed-in-to
interface, and any supplied serialization steps and deserialization steps for the partial interface or mixin should be understood as being appended to those of
the original or mixed-in-to interface.
Person
, which had
associated with it two pieces of associated data:
-
a name value, which is a string;
-
and a best friend value, which is either another
Person
instance or null
We could then define Person
instances to be serializable objects by
annotating the Person
interface with the [Serializable]
extended attribute, and defining the following accompanying algorithms:
- serialization steps
-
-
Set serialized.[[Name]] to value’s associated name value.
-
Let serializedBestFriend be the sub-serialization of value’s associated best friend value.
-
Set serialized.[[BestFriend]] to serializedBestFriend.
-
- deserialization steps
-
-
Set value’s associated name value to serialized.[[Name]].
-
Let deserializedBestFriend be the sub-deserialization of serialized.[[BestFriend]].
-
Set value’s associated best friend value to deserializedBestFriend.
-
Objects defined in the JavaScript specification are handled by the StructuredSerialize abstract operation directly.
Originally, this specification defined the concept of "cloneable objects", which could be cloned from one JavaScript Realm to another. However, to better specify the behavior of certain more complex situations, the model was updated to make the serialization and deserialization explicit.
2.9.2. Transferable objects
Transferable objects support being transferred across event loops. Transferring is effectively recreating the object while sharing a reference to the underlying data and then detaching the object being transferred. This is useful to transfer ownership of expensive resources. Not all objects are transferable objects and not all aspects of objects that are transferable objects are necessarily preserved when transferred.
Transferring is an irreversible and non-idempotent operation. Once an object has been transferred, it cannot be transferred, or indeed used, again.
Platform objects can be transferable objects if they implement only interfaces decorated with the [Transferable]
IDL extended attribute. Such interfaces must also define the following algorithms:
- transfer steps, taking a platform object value and a Record dataHolder
-
A set of steps that transfers the data in value into fields of dataHolder. The resulting data held in dataHolder must be independent of any JavaScript Realm.
These steps may throw an exception if transferral is not possible.
- transfer-receiving steps, taking a Record dataHolder and a platform object value
-
A set of steps that receives the data in dataHolder, using it to set up value as appropriate. value will be a newly-created instance of the platform object type in question, with none of its internal data set up; setting that up is the job of these steps.
These steps may throw an exception if it is not possible to receive the transfer.
It is up to the definition of individual platform objects to determine what data is transferred by these steps. Typically the steps are very symmetric.
The [Transferable]
extended attribute must take no
arguments, and must not appear on anything other than an interface. It must appear only once on an
interface. It must not be used on a callback interface. If it appears on a partial interface or an
interface that is really a mixin, then it must also appear on the original or mixed-in-to
interface, and any supplied serialization steps and deserialization steps for the partial interface or mixin should be understood as being appended to those of
the original or mixed-in-to interface.
Platform objects that are transferable objects have a Detached internal slot. This is used to ensure that once a platform object has been transferred, it cannot be transferred again.
Objects defined in the JavaScript specification are handled by the StructuredSerializeWithTransfer abstract operation directly.
2.9.3. StructuredSerializeInternal ( value, forStorage [ , memory ] )
The StructuredSerializeInternal abstract operation takes as input a JavaScript value value and serializes it to a Realm-independent form, represented here as a Record. This serialized form has all the information necessary to later deserialize into a new JavaScript value in a different Realm.
This process can throw an exception, for example when trying to serialize un-serializable objects.
-
If memory was not supplied, let memory be an empty map.
The purpose of the memory map is to avoid serializing objects twice. This ends up preserving cycles and the identity of duplicate objects in graphs.
-
If memory[value] exists, then return memory[value].
-
Let deep be false.
-
If Type(value) is Undefined, Null, Boolean, String, or Number, then return { [[Type]]: "primitive", [[Value]]: value }.
-
If Type(value) is Symbol, then throw a "
DataCloneError
"DOMException
. -
Let serialized be an uninitialized value.
-
If value has a [[BooleanData]] internal slot, then set serialized to { [[Type]]: "Boolean", [[BooleanData]]: value.[[BooleanData]] }.
-
Otherwise, if value has a [[NumberData]] internal slot, then set serialized to { [[Type]]: "Number", [[NumberData]]: value.[[NumberData]] }.
-
Otherwise, if value has a [[StringData]] internal slot, then set serialized to { [[Type]]: "String", [[StringData]]: value.[[StringData]] }.
-
Otherwise, if value has a [[DateValue]] internal slot, then set serialized to { [[Type]]: "Date", [[DateValue]]: value.[[DateValue]] }.
-
Otherwise, if value has a [[RegExpMatcher]] internal slot, then set serialized to { [[Type]]: "RegExp", [[RegExpMatcher]]: value.[[RegExpMatcher]], [[OriginalSource]]: value.[[OriginalSource]], [[OriginalFlags]]: value.[[OriginalFlags]] }.
-
Otherwise, if value has an [[ArrayBufferData]] internal slot, then:
-
Let size be value.[[ArrayBufferByteLength]].
-
If ! IsSharedArrayBuffer(value) is true, then:
-
If forStorage is true, then throw a "
DataCloneError
"DOMException
. -
Set serialized to { [[Type]]: "SharedArrayBuffer", [[ArrayBufferData]]: value.[[ArrayBufferData]], [[ArrayBufferByteLength]]: size, [[AgentCluster]]: the current Realm Record’s corresponding agent cluster }.
-
-
Otherwise:
-
If ! IsDetachedBuffer(value) is true, then throw a "
DataCloneError
"DOMException
. -
Let dataCopy be ? CreateByteDataBlock(size).
This can throw a
RangeError
exception upon allocation failure. -
Perform ! CopyDataBlockBytes(dataCopy, 0, value.[[ArrayBufferData]], 0, size).
-
Set serialized to { [[Type]]: "ArrayBuffer", [[ArrayBufferData]]: dataCopy, [[ArrayBufferByteLength]]: size }.
-
-
-
Otherwise, if value has a [[ViewedArrayBuffer]] internal slot, then:
-
Let buffer be the value of value’s [[ViewedArrayBuffer]] internal slot.
-
Let bufferSerialized be ? StructuredSerializeInternal(buffer, forStorage, memory).
-
Assert: bufferSerialized.[[Type]] is "ArrayBuffer".
-
If value has a [[DataView]] internal slot, then set serialized to { [[Type]]: "ArrayBufferView", [[Constructor]]: "DataView", [[ArrayBufferSerialized]]: bufferSerialized, [[ByteLength]]: value.[[ByteLength]], [[ByteOffset]]: value.[[ByteOffset]] }.
-
Otherwise:
-
Assert: value has a [[TypedArrayName]] internal slot.
-
Set serialized to { [[Type]]: "ArrayBufferView", [[Constructor]]: value.[[TypedArrayName]], [[ArrayBufferSerialized]]: bufferSerialized, [[ByteLength]]: value.[[ByteLength]], [[ByteOffset]]: value.[[ByteOffset]], [[ArrayLength]]: value.[[ArrayLength]] }.
-
-
-
Otherwise, if value has [[MapData]] internal slot, then:
-
Set serialized to { [[Type]]: "Map", [[MapData]]: a new empty List }.
-
Set deep to true.
-
-
Otherwise, if value has [[SetData]] internal slot, then:
-
Set serialized to { [[Type]]: "Set", [[SetData]]: a new empty List }.
-
Set deep to true.
-
-
Otherwise, if value is an Array exotic object, then:
-
Let valueLenDescriptor be ? OrdinaryGetOwnProperty(value, "
length
"). -
Let valueLen be valueLenDescriptor.[[Value]].
-
Set serialized to { [[Type]]: "Array", [[Length]]: valueLen, [[Properties]]: a new empty List }.
-
Set deep to true.
-
-
Otherwise, if value is a platform object that is a serializable object:
-
If value has a [[Detached]] internal slot whose value is true, then throw a "
DataCloneError
"DOMException
. -
Let typeString be the identifier of the primary interface of value.
-
Set serialized to { [[Type]]: typeString }.
-
Set deep to true.
-
-
Otherwise, if value is a platform object, then throw a "
DataCloneError
"DOMException
. -
Otherwise, if IsCallable(value) is true, then throw a "
DataCloneError
"DOMException
. -
Otherwise, if value has any internal slot other than [[Prototype]] or [Extensible], then throw a "
DataCloneError
"DOMException
.For instance, a [[PromiseState]] or [[WeakMapData]] internal slot.
-
Otherwise, if value is an exotic object, then throw a "
DataCloneError
"DOMException
. -
Otherwise:
-
Set serialized to { [[Type]]: "Object", [[Properties]]: a new empty List }.
-
Set deep to true.
-
-
Set memory[value] to serialized.
-
If deep is true, then:
-
If value has a [[MapData]] internal slot, then:
-
Let copiedList be a new empty List.
-
For each Record { [[Key]], [[Value]] } entry of value.[[MapData]]:
-
For each Record { [[Key]], [[Value]] } entry of copiedList:
-
Let serializedKey be ? StructuredSerializeInternal(entry.[[Key]], forStorage, memory).
-
Let serializedValue be ? StructuredSerializeInternal(entry.[[Value]], forStorage, memory).
-
Append { [[Key]]: serializedKey, [[Value]]: serializedValue } to serialized.[[MapData]].
-
-
-
Otherwise, if value has a [[SetData]] internal slot, then:
-
Let copiedList be a new empty List.
-
For each entry of value.[[SetData]]:
-
If entry is not the special value empty, append entry to copiedList.
-
-
For each entry of copiedList:
-
Let serializedEntry be ? StructuredSerializeInternal(entry, forStorage, memory).
-
Append serializedEntry to serialized.[[SetData]].
-
-
-
Otherwise, if value is a platform object that is a serializable object, then perform the appropriate serialization steps given value, serialized, and forStorage.
The serialization steps may need to perform a sub-serialization. This is an operation which takes as input a value subValue, and returns StructuredSerializeInternal(subValue, forStorage, memory). (In other words, a sub-serialization is a specialization of StructuredSerializeInternal to be consistent within this invocation.)
-
Otherwise:
-
Let enumerableKeys be a new empty List.
-
For each key in ! value.[[OwnPropertyKeys]]():
-
For each key in enumerableKeys:
-
If ! HasOwnProperty(value, key) is true, then:
-
Let inputValue be ? value.[[Get]](key, value).
-
Let outputValue be ? StructuredSerializeInternal(inputValue, forStorage, memory).
-
Append { [[Key]]: key, [[Value]]: outputValue } to serialized.[[Properties]].
-
-
-
The key collection performed above is very similar to the JavaScript specification’s EnumerableOwnProperties operation, but crucially it uses the deterministic ordering provided by the [[OwnPropertyKeys]] internal method, instead of reordering the keys in an unspecified manner as EnumerableOwnProperties does. [ECMA-262]
-
-
Return serialized.
const o = {};o.myself = o;
it produces the following result:
{ \[[Type]]: "Object", \[[Properties]]: « { \[[Key]]: "myself", \[[Value]]: <a pointer to this whole structure> } » }
2.9.4. StructuredSerialize ( value )
-
Return ? StructuredSerializeInternal(value, false).
2.9.5. StructuredSerializeForStorage ( value )
-
Return ? StructuredSerializeInternal(value, true).
2.9.6. StructuredDeserialize ( serialized, targetRealm [ , memory ] )
The StructuredDeserialize abstract operation takes as input a Record serialized, which was previously produced by StructuredSerialize or StructuredSerializeForStorage, and deserializes it into a new JavaScript value, created in targetRealm.
This process can throw an exception, for example when trying to allocate memory for the new
objects (especially ArrayBuffer
objects).
-
If memory was not supplied, let memory be an empty map.
The purpose of the memory map is to avoid deserializing objects twice. This ends up preserving cycles and the identity of duplicate objects in graphs.
-
If memory[serialized] exists, then return memory[serialized].
-
Let deep be false.
-
Let value be an uninitialized value.
-
If serialized contains a [[TransferConsumed]] field, then:
-
Assert: serialized.[[TransferConsumed]] is false. (It must be impossible to get in a situation where StructuredDeserialize is being called multiple times on the same serialization, if that serialization contains transfer data holders.)
-
Set serialized.[[TransferConsumed]] to true.
-
If serialized.[[Type]] is "ArrayBuffer", then set value to a new ArrayBuffer object in targetRealm whose [[ArrayBufferData]] internal slot value is serialized.[[ArrayBufferData]], and whose [[ArrayBufferByteLength]] internal slot value is serialized.[[ArrayBufferByteLength]].
In cases where the original memory occupied by [[ArrayBufferData]] is accessible during the deserialization, this step is unlikely to throw an exception, as no new memory needs to be allocated: the memory occupied by [[ArrayBufferData]] is instead just getting transferred into the new ArrayBuffer. This could be true, for example, when both the source and target Realms are in the same process.
-
Otherwise:
-
Let interfaceName be serialized.[[Type]].
-
If the interface identified by interfaceName is not exposed in targetRealm, then throw a "
DataCloneError
"DOMException
. -
Set value to a new instance of the interface identified by interfaceName, created in targetRealm.
-
Perform the appropriate transfer-receiving steps for the interface identified by interfaceName given serialized and value.
-
-
-
Otherwise, if serialized.[[Type]] is "primitive", then set value to serialized.[[Value]].
-
Otherwise, if serialized.[[Type]] is "Boolean", then set value to a new Boolean object in targetRealm whose [[BooleanData]] internal slot value is serialized.[[BooleanData]].
-
Otherwise, if serialized.[[Type]] is "Number", then set value to a new Number object in targetRealm whose [[NumberData]] internal slot value is serialized.[[NumberData]].
-
Otherwise, if serialized.[[Type]] is "String", then set value to a new String object in targetRealm whose [[StringData]] internal slot value is serialized.[[StringData]].
-
Otherwise, if serialized.[[Type]] is "Date", then set value to a new Date object in targetRealm whose [[DateValue]] internal slot value is serialized.[[DateValue]].
-
Otherwise, if serialized.[[Type]] is "RegExp", then set value to a new RegExp object in targetRealm whose [[RegExpMatcher]] internal slot value is serialized.[[RegExpMatcher]], whose [[OriginalSource]] internal slot value is serialized.[[OriginalSource]], and whose [[OriginalFlags]] internal slot value is serialized.[[OriginalFlags]].
-
Otherwise, if serialized.[[Type]] is "SharedArrayBuffer", then:
-
If targetRealm’s corresponding agent cluster is not serialized.[[AgentCluster]], then then throw a "
DataCloneError
"DOMException
. -
Otherwise, set value to a new SharedArrayBuffer object in targetRealm whose [[ArrayBufferData]] internal slot value is serialized.[[ArrayBufferData]] and whose [[ArrayBufferByteLength]] internal slot value is serialized.[[ArrayBufferByteLength]].
-
-
Otherwise, if serialized.[[Type]] is "ArrayBuffer", then set value to a new ArrayBuffer object in targetRealm whose [[ArrayBufferData]] internal slot value is serialized.[[ArrayBufferData]], and whose [[ArrayBufferByteLength]] internal slot value is serialized.[[ArrayBufferByteLength]].
If this throws an exception, then throw a "
DataCloneError
"DOMException
.This step might throw an exception if there is not enough memory available to create such an ArrayBuffer object.
-
Otherwise, if serialized.[[Type]] is "ArrayBufferView", then:
-
Let deserializedArrayBuffer be ? StructuredDeserialize(serialized.[[ArrayBufferSerialized]], targetRealm, memory).
-
If serialized.[[Constructor]] is "DataView", then set value to a new DataView object in targetRealm whose [[ViewedArrayBuffer]] internal slot value is deserializedArrayBuffer, whose [[ByteLength]] internal slot value is serialized.[[ByteLength]], and whose [[ByteOffset]] internal slot value is serialized.[[ByteOffset]].
-
Otherwise, set value to a new typed array object in targetRealm, using the constructor given by serialized.[[Constructor]], whose [[ViewedArrayBuffer]] internal slot value is deserializedArrayBuffer, whose \[TypedArrayName]] internal slot value is serialized.[[Constructor]], whose [[ByteLength]] internal slot value is serialized.[[ByteLength]], whose [[ByteOffset]] internal slot value is serialized.[[ByteOffset]], and whose [[ArrayLength]] internal slot value is serialized.[[ArrayLength]].
-
-
Otherwise, if serialized.[[Type]] is "Map", then:
-
Set value to a new Map object in targetRealm whose [[MapData]] internal slot value is a new empty List.
-
Set deep to true.
-
-
Otherwise, if serialized.[[Type]] is "Set", then:
-
Set value to a new Set object in targetRealm whose [[SetData]] internal slot value is a new empty List.
-
Set deep to true.
-
-
Otherwise, if serialized.[[Type]] is "Array", then:
-
Let outputProto be the %ArrayPrototype% intrinsic object in targetRealm.
-
Set value to ! ArrayCreate(serialized.[[Length]], outputProto).
-
Set deep to true.
-
-
Otherwise, if serialized.[[Type]] is "Object", then:
-
Set value to a new Object in targetRealm.
-
Set deep to true.
-
-
Otherwise:
-
Let interfaceName be serialized.[[Type]].
-
If the interface identified by interfaceName is not exposed in targetRealm, then throw a "
DataCloneError
"DOMException
. -
Set value to a new instance of the interface identified by interfaceName, created in targetRealm.
-
Set deep to true.
-
-
Set memory[serialized] to value.
-
If deep is true, then:
-
If serialized.[[Type]] is "Map", then:
-
For each Record { [[Key]], [[Value]] } entry of serialized.[[MapData]]:
-
Let deserializedKey be ? StructuredDeserialize(entry.[[Key]], targetRealm, memory).
-
Let deserializedValue be ? StructuredDeserialize(entry.[[Value]], targetRealm, memory).
-
Append { [[Key]]: deserializedKey, [Value]]: deserializedValue } to value.[[MapData]].
-
-
-
Otherwise, if serialized.[[Type]] is "Set", then:
-
For each entry of serialized.[[SetData]]:
-
Let deserializedEntry be ? StructuredDeserialize(entry, targetRealm, memory).
-
Append deserializedEntry to value.[[SetData]].
-
-
-
Otherwise, if serialized.[[Type]] is "Array" or "Object", then:
-
For each Record { [[Key]], [[Value]] } entry of serialized.[[Properties]]:
-
Let deserializedValue be ? StructuredDeserialize(entry.[[Value]], targetRealm, memory).
-
Let result be ! CreateDataProperty(value, entry.[[Key]], deserializedValue).
-
Assert: result is true.
-
-
-
Otherwise:
-
Perform the appropriate deserialization steps for the interface identified by serialized.[[Type]], given serialized and value.
The deserialization steps may need to perform a sub-deserialization. This is an operation which takes as input a previously-serialized Record subSerialized, and returns StructuredDeserialize(subSerialized, targetRealm, memory). (In other words, a sub-deserialization is a specialization of StructuredDeserialize to be consistent within this invocation.)
-
-
-
Return value.
2.9.7. StructuredSerializeWithTransfer ( value, transferList )
-
Let memory be an empty map.
In addition to how it is used normally by StructuredSerializeInternal, in this algorithm memory is also used to ensure that StructuredSerializeInternal ignores items in transferList, and let us do our own handling instead.
-
For each transferable of transferList:
-
If transferable has neither an [[ArrayBufferData]] internal slot nor a [[Detached]] internal slot, then throw a "
DataCloneError
"DOMException
. -
If transferable has an [[ArrayBufferData]] internal slot and either ! IsSharedArrayBuffer(transferable) is true or ! IsDetachedBuffer(transferable) is true, then throw a "
DataCloneError
"DOMException
. -
If transferable has a [[Detached]] internal slot and transferable.[[Detached]] is true, then throw a "
DataCloneError
"DOMException
. -
Let placeholder be a user-agent-defined placeholder object.
-
Set memory[transferable] to placeholder.
-
-
Let serialized be ? StructuredSerializeInternal(value, false, memory).
-
Let transferDataHolders be a new empty List.
-
For each transferable of transferList:
-
Let placeholder be memory[transferable].
-
Let dataHolder be an uninitialized value.
-
If transferable has an [[ArrayBufferData]] internal slot, then:
-
Set dataHolder to { [[TransferConsumed]]: false, [[Type]]: "ArrayBuffer", [[ArrayBufferData]]: transferable.[[ArrayBufferData]], [[ArrayBufferByteLength]]: transferable.[[ArrayBufferByteLength]] }.
-
Perform ! DetachArrayBuffer(transferable).
-
-
Otherwise:
-
Assert: transferable is a platform object that is a transferable object.
-
Let interfaceName be the identifier of the primary interface of transferable.
-
Set dataHolder to { [[TransferConsumed]]: false, [[Type]]: interfaceName }.
-
Perform the appropriate transfer steps for the interface identified by interfaceName, given transferable and dataHolder.
-
Set transferable.[[Detached]] to true.
-
-
Within serialized, replace all instances of placeholder with dataHolder.
-
Append dataHolder to transferDataHolders.
-
-
Return { [[Serialized]]: serialized, [[TransferDataHolders]]: transferDataHolders }.
2.9.8. StructuredDeserializeWithTransfer ( serializeWithTransferResult, targetRealm )
-
Let memory be an empty map.
In addition to how it is used normally by StructuredDeserialize, in this algorithm memory is also used to help us determine the list of transferred values.
-
Let deserialized be ? StructuredDeserialize(serializeWithTransferResult.[[Serialized]], targetRealm, memory).
-
Let transferredValues be a new empty List.
-
For each transferDataHolder of serializeWithTransferResult.[[TransferDataHolders]]:
-
Append memory[transferDataHolder] to transferredValues.
-
-
Return { [[Deserialized]]: deserialized, [[TransferredValues]]: transferredValues }.
2.9.9. Performing serialization and transferring from other specifications
Other specifications may use the abstract operations defined here. The following provides some guidance on when each abstract operation is typically useful, with examples.
- StructuredSerializeWithTransfer
- StructuredDeserializeWithTransfer
-
Cloning a value to another JavaScript Realm, with a transfer list, but where the target Realm is not known ahead of time. In this case the serialization step can be performed immediately, with the deserialization step delayed until the target Realm becomes known.
messagePort.postMessage()
uses this pair of abstract operations, as the destination Realm is not known until theMessagePort
has been shipped. - StructuredSerialize
- StructuredSerializeForStorage
- StructuredDeserialize
-
Creating a JavaScript Realm-independent snapshot of a given value which can be saved for an indefinite amount of time, and then reified back into a JavaScript value later, possibly multiple times.
StructuredSerializeForStorage can be used for situations where the serialization is anticipated to be stored in a persistent manner, instead of passed between Realms. It throws when attempting to serialize
SharedArrayBuffer
objects, since storing shared memory does not make sense. Similarly, it can throw or possibly have different behavior when given a platform object with custom serialization steps when the forStorage argument is true.history.pushState()
andhistory.replaceState()
use StructuredSerializeForStorage on author-supplied state objects, storing them as serialized state in the appropriate session history entry. Then, StructuredDeserialize is used so that thehistory.state
property can return a clone of the originally-supplied state object.broadcastChannel.postMessage()
uses StructuredSerialize on its input, then uses StructuredDeserialize multiple times on the result to produce a fresh clone for each destination being broadcast to. Note that transferring does not make sense in multi-destination situations.Any API for persisting JavaScript values to the filesystem would also use StructuredSerializeForStorage on its input and StructuredDeserialize on its output.
In general, call sites may pass in Web IDL values instead of JavaScript values; this is to be understood to perform an implicit conversion to the JavaScript value before invoking these algorithms.
This specification used to define a "structured clone" algorithm, and more recently a StructuredClone abstract operation. However, in practice all known uses of it were better served by separate serialization and deserialization steps, so it was removed.
Call sites that are not invoked as a result of author code synchronously calling into a user agent method must take care to properly prepare to run script and prepare to run a callback before invoking StructuredSerialize, StructuredSerializeForStorage, or StructuredSerializeWithTransfer abstract operations, if they are being performed on arbitrary objects. This is necessary because the serialization process can invoke author-defined accessors as part of its final deep-serialization steps, and these accessors could call into operations that rely on the entry and incumbent concepts being properly set up.
window.postMessage()
performs StructuredSerializeWithTransfer on its arguments, but is careful to do so
immediately, inside the synchronous portion of its algorithm. Thus it is able to use the
algorithms without needing to prepare to run script and prepare to run a callback.
In contrast, a hypothetical API that used StructuredSerialize to serialize some author-supplied object periodically, directly from a task on the event loop, would need to ensure it performs the appropriate preparations beforehand. As of this time, we know of no such APIs on the platform; usually it is simpler to perform the serialization ahead of time, as a synchronous consequence of author code.
2.9.10. Monkey patch for Blob
and FileList
objects
This monkey patch will be moved in due course. See w3c/FileAPI issue 32.
Blob
objects are serializable objects. The Blob
interface must be annotated with the [Serializable]
extended attribute. Their serialization steps, given value and serialized, are:
-
Set serialized.[[SnapshotState]] to value’s snapshot state.
-
Set serialized.[[ByteSequence]] to value’s underlying byte sequence.
Their deserialization steps, given serialized and value, are:
-
Set value’s snapshot state to serialized.[[SnapshotState]].
-
Set value’s underlying byte sequence to serialized.[[ByteSequence]].
File
objects are serializable objects. The File
interface must be annotated with the [Serializable]
extended attribute. Their serialization steps, given value and serialized, are:
-
Set serialized.[[SnapshotState]] to value’s snapshot state.
-
Set serialized.[[ByteSequence]] to value’s underlying byte sequence.
-
Set serialized.[[Name]] to the value of value’s
name
attribute. -
Set serialized.[[LastModified]] to the value of value’s
lastModified
attribute.
Their deserialization steps, given serialized and value, are:
-
Set value’s snapshot state to serialized.[[SnapshotState]].
-
Set value’s underlying byte sequence to serialized.[[ByteSequence]].
-
Initialize the value of value’s
name
attribute to serialized.[[Name]]. -
Initialize the value of value’s
lastModified
attribute to serialized.[[LastModified]].
FileList
objects are serializable objects. The FileList
interface must be annotated with the [Serializable]
extended attribute. Their serialization steps, given value and serialized, are:
-
Set serialized.[[Files]] to an empty list.
-
For each file in value, append the sub-serialization of file to serialized.[[Files]].
Their deserialization steps, given serialized and value, are:
-
For each file of serialized.[[Files]], add the sub-deserialization of file to value.