A vocabulary and associated APIs for HTML and XHTML
This section only describes the rules for XML resources. Rules for
text/html resources are discussed in the section above entitled "The HTML
The syntax for using HTML with XML, whether in XHTML documents or embedded in other XML documents, is defined in the XML and Namespaces in XML specifications. [XML] [XMLNS]
This specification does not define any syntax-level requirements beyond those defined for XML proper.
XML documents may contain a
DOCTYPE if desired, but this is not required to
conform to this specification. This specification does not define a public or system identifier,
nor provide a formal DTD.
According to the XML specification, XML processors are not guaranteed to process
the external DTD subset referenced in the DOCTYPE. This means, for example, that using entity references for characters in XHTML documents
is unsafe if they are defined in an external file (except for
This section describes the relationship between XML and the DOM, with a particular emphasis on how this interacts with HTML.
An XML parser, for the purposes of this specification, is a construct that follows
the rules given in the XML specification to map a string of bytes or characters into a
At the time of writing, no such rules actually exist.
An XML parser is either associated with a
Document object when it is
created, or creates one implicitly.
Document must then be populated with DOM nodes that represent the tree
structure of the input passed to the parser, as defined by the XML specification, the Namespaces
in XML specification, and the DOM specification. DOM mutation events must not fire for the
operations that the XML parser performs on the
Document's tree, but the
user agent must act as if elements and attributes were individually appended and set respectively
so as to trigger rules in this specification regarding what happens when an element is inserted
into a document or has its attributes set, and the DOM specification's requirements regarding
mutation observers mean that mutation observers are fired (unlike mutation events). [XML] [XMLNS] [DOM] [DOMEVENTS]
Between the time an element's start tag is parsed and the time either the element's end tag is parsed or the parser detects a well-formedness error, the user agent must act as if the element was in a stack of open elements.
This is used by the
object element to avoid instantiating plugins
param element children have been parsed.
This specification provides the following additional information that user agents should use when retrieving an external entity: the public identifiers given in the following list all correspond to the URL given by this link. (This URL is a DTD containing the entity declarations for the names listed in the named character references section.) [XML]
-//W3C//DTD XHTML 1.0 Transitional//EN
-//W3C//DTD XHTML 1.1//EN
-//W3C//DTD XHTML 1.0 Strict//EN
-//W3C//DTD XHTML 1.0 Frameset//EN
-//W3C//DTD XHTML Basic 1.0//EN
-//W3C//DTD XHTML 1.1 plus MathML 2.0//EN
-//W3C//DTD XHTML 1.1 plus MathML 2.0 plus SVG 1.1//EN
-//W3C//DTD MathML 2.0//EN
-//WAPFORUM//DTD XHTML Mobile 1.0//EN
Furthermore, user agents should attempt to retrieve the above external entity's content when one of the above public identifiers is used, and should not attempt to retrieve any other external entity's content.
This is not strictly a violation of the XML specification, but it does contradict the spirit of the XML specification's requirements. This is motivated by a desire for user agents to all handle entities in an interoperable fashion without requiring any network access for handling external subsets. [XML]
When an XML parser creates a
script element, it
must be marked as being "parser-inserted" and its "force-async" flag
must be unset. If the parser was originally created for the XML fragment parsing
algorithm, then the element must be marked as "already started" also. When the
element's end tag is parsed, the user agent must perform a microtask checkpoint,
provide a stable state, and then prepare the
script element. If this causes there to be a pending parsing-blocking
script, then the user agent must run the following steps:
Block this instance of the XML parser, such that the event loop will not run tasks that invoke it.
Spin the event loop until the parser's
Document has no
style sheet that is blocking scripts and the pending parsing-blocking
script's "ready to be parser-executed" flag is set.
Unblock this instance of the XML parser, such that tasks that invoke it can again be run.
There is no longer a pending parsing-blocking script.
document.write() API is not
available for XML documents, much of the complexity in the HTML parser
is not needed in the XML parser.
When an XML parser would append a node to a
template element, it must instead append it to the
template contents (a
This is a willful violation of the XML specification; unfortunately,
XML is not formally extensible in the manner that is needed for
When an XML parser creates a
Node object, its
ownerDocument must be set to the
the node into which the newly created node is to be inserted.
Certain algorithms in this specification spoon-feed the parser characters one string at a time. In such cases, the XML parser must act as it would have if faced with a single string consisting of the concatenation of all those characters.
When an XML parser reaches the end of its input, it must stop parsing, following the same rules as the HTML parser. An XML parser can also be aborted, which must again by done in the same way as for an HTML parser.
For the purposes of conformance checkers, if a resource is determined to be in the XHTML syntax, then it is an XML document.
The XML fragment serialization algorithm for a
Element node either returns a fragment of XML that represents that node or throws an
Documents, the algorithm must return a string in the form of a document entity, if none of the error cases
Elements, the algorithm must return a string in the form of an internal general parsed entity, if none of the
error cases below apply.
In both cases, the string returned must be XML namespace-well-formed and must be an isomorphic
serialization of all of that node's relevant child nodes, in tree order.
User agents may adjust prefixes and namespace declarations in the serialization (and indeed might
be forced to do so in some cases to obtain namespace-well-formed XML). User agents may use a
combination of regular text and character references to represent
Text nodes in the
A node's relevant child nodes are those that apply given the following rules:
templateelement's template contents, if any.
Elements, if any of the elements in the serialization are in no namespace, the
default namespace in scope for those elements must be explicitly declared as the empty string. (This doesn't apply in the
Document case.) [XML]
For the purposes of this section, an internal general parsed entity is considered XML namespace-well-formed if a document consisting of an element with no namespace declarations whose contents are the internal general parsed entity would itself be XML namespace-well-formed.
If any of the following error cases are found in the DOM subtree being serialized, then the
algorithm must throw an
InvalidStateError exception instead of returning a
Documentnode with no child element nodes.
DocumentTypenode that has an external subset public identifier that contains characters that are not matched by the XML
DocumentTypenode that has an external subset system identifier that contains both a """ (U+0022) and a "'" (U+0027) or that contains characters that are not matched by the XML
Attrnode with no namespace whose local name is the lowercase string "
Elementnode with two or more attributes with the same local name and namespace.
ProcessingInstructionnode whose data contains characters that are not matched by the XML
Commentnode whose data contains two adjacent U+002D HYPHEN-MINUS characters (-) or ends with such a character.
ProcessingInstructionnode whose target name is an ASCII case-insensitive match for the string "
ProcessingInstructionnode whose target name contains a ":" (U+003A).
ProcessingInstructionnode whose data contains the string "
These are the only ways to make a DOM unserializable. The DOM enforces all the
other XML constraints; for example, trying to append two elements to a
will throw a
When the algorithm must produce a serialization of a
template element, the string
returned must contain a serialization of the child nodes of the template element's
DocumentFragment, rather than the
template element's children.
The XML fragment parsing algorithm either returns a
Document or throws
SyntaxError exception. Given a string input and an optional
context element context, the algorithm is as
Create a new XML parser.
If there is a context element, feed the parser just created the string corresponding to the start tag of that element, declaring all the namespace prefixes that are in scope on that element in the DOM, as well as declaring the default namespace (if any) that is in scope on that element in the DOM.
A namespace prefix is in scope if the DOM
on the element would return a non-null value for that prefix.
The default namespace is the namespace for which the DOM
isDefaultNamespace() method on the element would return true.
If there is a context element, no
DOCTYPE is passed to the parser, and therefore no external subset is
referenced, and therefore no entities will be recognized.
Feed the parser just created the string input.
If there is a context element, feed the parser just created the string corresponding to the end tag of that element.
If there is an XML well-formedness or XML namespace well-formedness error, then throw a
SyntaxError exception and abort these steps.
If there is a context element, and the root
element of the resulting
Document has any sibling nodes, then throw a
SyntaxError exception and abort these steps.
If there is a context element, then return the
child nodes of the root element of the resulting
Document, in tree
Otherwise, return the children of the
Document object, in tree