Copyright © 2015 W3C® (MIT, ERCIM, Keio, Beihang). W3C liability, trademark and document use rules apply.
This specification defines a JSON-based manifest that provides developers with a centralized place to put metadata associated with a web application. This includes, but is not limited to, the web application's name, links to icons, as well as the preferred URL to open when a user launches the web application. The manifest also allows developers to declare a default orientation for their web application, as well as providing the ability to set the display mode for the application (e.g., in fullscreen). Additionally, the manifest allows a developer to "scope" a web application to a URL. This restricts the URLs to which the application can be navigated and provides a means to "deep link" into a web application from other applications.
Using this metadata, user agents can provide developers with means to create user experiences that are more comparable to that of a native application.
In addition, this specification defines the manifest
link
type, which provides a declarative means for a document to be
associated with a manifest.
This section describes the status of this document at the time of its publication. Other documents may supersede this document. A list of current W3C publications and the latest revision of this technical report can be found in the W3C technical reports index at http://www.w3.org/TR/.
Implementors need to be aware that this specification is starting to stabilize. Aspects of this specification are shipping in at least one browser (see links to implementation status at the top of this document). Implementors who are not taking part in the discussions will find the specification changing out from under them in incompatible ways. Vendors interested in implementing this specification before it eventually reaches the Candidate Recommendation phase should subscribe to the repository on GitHub and take part in the discussions.
This Working Draft is intended to meet the wide review requirements as defined in the 2014 Process Document. The deadline for comments is 5 March 2015. The next anticipated publication of this specification is a Candidate Recommendation. See Issue 308 for the specification's Candidate Recommendation status.
This document was published by the Web Applications (WebApps) Working Group as a Working Draft. This document is intended to become a W3C Recommendation. If you wish to make comments regarding this document, please send them to public-webapps@w3.org (subscribe, archives). All comments are welcome.
Publication as a Working Draft does not imply endorsement by the W3C Membership. This is a draft document and may be updated, replaced or obsoleted by other documents at any time. It is inappropriate to cite this document as other than work in progress.
This document was produced by a group operating under the 5 February 2004 W3C Patent Policy. W3C maintains a public list of any patent disclosures made in connection with the deliverables of the group; that page also includes instructions for disclosing a patent. An individual who has actual knowledge of a patent which the individual believes contains Essential Claim(s) must disclose the information in accordance with section 6 of the W3C Patent Policy.
This document is governed by the 1 August 2014 W3C Process Document.
link
and meta
elements
This section is non-normative.
This section shows how developers can make use of the various features of this specification.
This section is non-normative.
The following shows a typical manifest.
{ "name": "Super Racer 2000", "short_name": "Racer2K", "icons": [{ "src": "icon/lowres", "sizes": "64x64", "type": "image/webp" }, { "src": "icon/hd_small", "sizes": "64x64" }, { "src": "icon/hd_hi", "sizes": "128x128", "density": 2 }], "scope": "/racer/", "start_url": "/racer/start.html", "display": "fullscreen", "orientation": "landscape" }
link
element to link to a manifest
This section is non-normative.
Example of using a link
element to associate a website
with a manifest. The example also shows how to use [HTML]'s
link
and meta
elements to give the web
application a fallback name and set of icons.
<!doctype> <html> <title>Store finder - search</title> <!-- Startup configuration --> <link rel="manifest" href="manifest.json"> <!-- Fallback application metadata for legacy browsers --> <meta name="application-name" content="Store Finder"> <link rel="icon" sizes="16x16 32x32 48x48" href="lo_def.ico"> <link rel="icon" sizes="512x512" href="hi_def.png">
This document attempts to address the Use Cases and Requirements for Installable Web Apps.
A web application is installed if the user agent has provided the end-user with a means of instantiating a new top-level browsing context that has the manifest's members applied to it. That is, the manifest's members, or their defaults, are in effect on the top-level browsing context (see application context).
An example of installing would be a user agent that allows the end-user to add a shortcut to a web application on their device's homescreen (using the name and one of the icons found in the manifest). Then, when the end-user launches a web application through this explicit means, the manifest is applied to the browsing context prior to the start URL being loaded. This gives the user agent time to apply the relevant values of the manifest, possibly changing the display mode and screen orientation of the web application. Alternatively, an application context can be launched through a deep link (a URL that is within scope of the installed web application); in which case, the manifest is applied and the deep link is loaded within the context of web application.
This section is non-normative.
By design, this specification does not provide developers with an explicit API to "install" a web application. Instead, a manifest can serve as an installability signal (amongst other signals) to a user agent that a web application can be installed.
Installability signals can include things like the ones in the following list (this list is not exhaustive and some items might not apply to all user agents). For instance, the web application:
name
member and
a suitable icon.
How a user agent makes use of these installability signals to determine if a web application is installable is left to implementers.
A display mode represents how developers would like the user agent to present the web application to a user (e.g., in fullscreen). Display modes correspond to user interface (UI) metaphors and functionality in use on a given platform. The UI conventions of the display modes are purely advisory and implementers are free to interpret them how they best see fit.
Once a user agent applies a particular display mode to an application context, it becomes the default display mode for the top-level browsing context (i.e., it is used as the display mode when the window is navigated). The user agent MAY override the default display mode for security reasons (e.g., the top-level browsing context is navigated to another origin) and/or the user agent MAY provide the user with a means of switching to another display mode.
When the display
member is missing, or if there is no
valid display
member, the user agent uses the
browser
display mode as the default display
mode. As such, the user agent is REQUIRED to support the
browser
display mode.
Each display mode, except browser
, has a recursive
fallback display mode, which is the display mode that
the user agent can try to use if it doesn't support a particular
display mode. If the user agent does support a fallback display
mode, then it checks to see if it can use that display mode's fallback
display mode. This creates a fallback chain, with the default
display mode (browser
) being the last item in the
chain.
For example, Awesome Browser only supports the
minimal-ui
and browser
display modes, but a
developer declares that she wants fullscreen
in the
manifest. In this case, the user agent will first check if it
supports fullscreen
(it doesn't), so it falls back to
standalone
(which it also doesn't support), and
ultimately falls back to minimal-ui
.
The display modes values and their corresponding fallback display modes are as follows:
fullscreen
is
standalone
.
standalone
is
minimal-ui
.
minimal-ui
is
browser
.
browser
display mode doesn't have a
fallback display mode (conforming user agents are required to
support the browser
display mode).
The fullscreen display mode is orthogonal to, and works
independently of, the [WHATWG-FULLSCREEN] API. The
fullscreen
display mode affects the
fullscreen state of the browser window, while the [WHATWG-FULLSCREEN]
API operates on an element contained within the viewport. As such, a
web application can have its display mode set to
fullscreen
, while
document.fullScreenElement
returns null
, and
fullscreenEnabled
returns false
.
'display-mode'
media feature
The display-mode
media feature represents,
via a CSS media query [MEDIAQ], the display mode that the
user agent is applying to the web application.
A user agent MUST reflect the applied display mode of the web application via a CSS media query [MEDIAQ].
An example in CSS:
@media all and (display-mode: minimal-ui) { /* ... */ } @media all and (display-mode: standalone) { /* ... */ }
Accessing the display-mode media feature in ECMAScript through
matchMedia()
of [cssom-view]:
let standalone = matchMedia( '(display-mode: standalone)' ); standalone.onchange = function(e) { /* handle changes to display mode */ } if (standalone.matches) { /* do standalone things */ }
The 'display-mode'
media feature allows an origin
access to aspects of a user’s local computing environment and,
together with the display
member, allows an origin
some measure of control over a user agent’s native UI: Through a
CSS media query, a script can know the display mode of a web
application. An attacker could, in such a case, exploit the fact
that an application is being displayed in fullscreen to mimic the
user interface of another application.
Furthermore, by neglecting to define a scope member in the manifest, it's possible to put a web application into a display mode that persists cross-origin (for legacy reasons, this is the default behavior). In case where the navigation scope is unbounded, it is left to the user agent to either stop applying the manifest when a cross-origin navigation occurs or to show some sort of security warning to the user.
A resource is said to be associated with a manifest if the
resource representation, an HTML document, has a manifest
link relationship.
The manifest
keyword can be used with a [HTML]
link
element. This keyword creates an external
resource link.
Link type | Effect on... | Brief description | |
---|---|---|---|
link
|
a and area
|
||
manifest
|
External Resource | not allowed | Imports or links to a manifest. |
The media type for a manifest serves as the default media type
for resources associated with the manifest
link type.
In cases where more than one link
element with a
manifest
link type appears in a Document
,
the user agent uses the first link
element in
tree order and ignores all subsequent link
element with a
manifest
link type (even if the first element was
erroneous). See the steps for obtaining a manifest.
To obtain a manifest, the user agent MUST run the steps for
obtaining a manifest. The appropriate time to obtain the manifest
is left up to implementations. A user agent MAY opt to delay fetching
a manifest until after the document and its other resources have been
fully loaded (i.e., to not delay the availability of content and
scripts required by the document
).
A manifest is obtained and applied regardless of the
media
attribute of the link
element matches the environment or not.
This section defines algorithms for obtaining, processing, and applying a manifest, and gives recommendations to implementers on how to react when the manifest is updated.
The steps for obtaining a manifest are given by the following algorithm. The algorithm, if successful, returns a processed manifest and the manifest URL; otherwise, it terminates prematurely and returns nothing. In the case of nothing being return, the user agent MUST ignore the manifest declaration. In running these steps, a user agent MUST NOT delay the load event.
Document
of the top-level browsing
context, let manifest link be the first
link
element in tree order whose
rel
attribute contains the token manifest
.
null
, terminate this
algorithm.
Authors are encouraged to use the HTTP cache directives to explicitly cache the manifest. For example, the following response would cause a cached manifest to be used one year from the time the response is sent:
HTTP/1.1 200 OK Cache-Control: max-age=31536000 Content-Type: application/manifest+json { "name": "Super Racer 2000", "start_url": "/start.html", "display": "fullscreen", "orientation": "landscape" }
A user agent MUST support [CSP2].
The manifest-src
and default-src
directives govern the origins from which a user agent can
fetch a manifest. As with other directives, by default the
manifest-src
directive is *
, meaning
that a user agent can, [CORS] permitting, fetch the manifest
cross-domain. Remote origins (e.g., a CDN) wanting to host
manifests for various web applications will need to include the
appropriate [CORS] response header in their HTTP response
(e.g., Access-Control-Allow-Origin:
https://example.com
).
When instructed to issue a developer warning, the user agent MAY report the conformance violation to the developer in a user-agent-specific manner (e.g., report the problem in an error console), or MAY ignore the error and do nothing.
When instructed to ignore, the user agent MUST act as if whatever manifest, member, or value caused the condition is absent.
The following algorithm provides an extension point: other specifications that add new members to the manifest are encouraged to hook themselves into this specification at this point in the algorithm.
The extension point is meant to help avoid issues related to monkey patching.
The steps for processing a manifest are given by the following algorithm. The algorithm takes a text string as an argument, which represents a manifest, and a URL manifest URL, which represents the location of the manifest, and a URL document URL. The output from inputting an JSON document into this algorithm is a processed manifest.
"{}"
.
"{}"
.
start_url
member with manifest,
manifest URL, and document URL as arguments.
display
member with manifest as the
argument.
orientation
member with manifest and
display mode as arguments.
name
member with manifest as the argument.
short_name
member with manifest as the
argument.
icons
member with manifest and manifest URL as
arguments.
scope
member with manifest, manifest URL,
document URL, start URL as arguments.
A manifest is applied to a top-level browsing context, meaning that the members of the manifest are affecting the presentation or behavior of a browsing context.
A top-level browsing context that has a manifest applied to it is referred to as an application context.
If an application context is created as a result of the user agent being asked to navigate to a deep link, the user agent MUST immediately navigate to the deep link with replacement enabled. Otherwise, when the application context is created, the user agent MUST immediately navigate to the start URL with replacement enabled.
Please note that the start URL is not necessarily the value of the start_url member: the user or user agent could have changed it when the application was added to home-screen or otherwise bookmarked.
The appropriate time to apply a manifest is when the application context is created and before navigation to the start URL begins.
By using the manifest URL, a user agent MAY periodically check if the contents of a manifest has been modified (e.g., by honoring HTTP cache directives associated with the manifest or by checking for updates after the web application has been launched). In the event that the members of the manifest have been updated, as determined by running the steps for processing a manifest and seeing if anything has changed, the user agent MAY update the metadata corresponding to the web application (e.g., by replacing the name, icons, navigation scope, or whatever other data has been changed).
In addition, even if the manifest has not been modified, the user agents MAY periodically check if resources referenced from a manifest (e.g., the icons) have been modified by honoring HTTP cache directives. If any resources have been modified, the user agent MAY replace any stale resources.
To avoid one application masquerading as another, it is RECOMMENDED that users be made aware of any such updates using implementation or platform specific conventions.
A manifest is a JSON document that contains startup parameters and application defaults for when a web application is launched. A manifest consists of a top-level object that contains zero or more members. Each of the members are defined below, as well as how their values are processed.
Every manifest has an associated manifest URL, which the [URL] from which the manifest was fetched.
name
member
The name
member is a
string that represents the name of the web
application as it is usually displayed to the user (e.g., amongst a
list of other applications, or as a label for an icon).
For all intents and purposes, the name
member is
functionally equivalent to having a meta
element
whose name attribute is
application-name
in a [HTML] document. In
cases where no suitable name can be derived from processing a
manifest, [HTML]'s application-name or the
title
element serve as suitable fallbacks.
The steps for processing the name
member is
given by the following algorithm. The algorithm takes a
manifest as an argument. This algorithm returns a string
or undefined
.
name
".
undefined
.
short_name
member
The short_name
member
is a string that represents a short
version of the name of the web application. It is intended to be used
where there is insufficient space to display the full name of the web
application.
The steps for processing the short_name
member is given by the following algorithm. The algorithm takes
a manifest as an argument. This algorithm returns a string
or undefined
.
short_name
".
undefined
.
scope
member
The scope
member is a
string that represents the navigation scope of this web application's
application context.
The steps for processing the scope
member is
given by the following algorithm. The algorithm takes a
manifest manifest, a URL manifest
URL, a URL document URL, and a URL start
URL. This algorithm returns a URL or
undefined
.
scope
".
undefined
", issue
a developer warning that the type is unsupported.
undefined
.
undefined
.
scope
needs to be
same-origin as Document
of the application
context.
undefined
.
undefined
.
icons
member
The icons
member is an
array of icon
objects that can serve as iconic representations of the web
application in various contexts. For example, they can be used to
represent the web application amongst a list of other applications,
or to integrate the web application with an OS's task switcher and/or system
preferences.
If no icons are listed in the manifest (or none of them are found to
be suitable during processing), it is RECOMMENDED that the user agent
fall back to using any icons found in the Document
of
the top-level browsing context. For example, an icon link
type and/or a favicon.ico
can serve as suitable
fallbacks.
The steps for processing the icons
member are
given by the following algorithm. The algorithm takes a manifest, and
a URL manifest URL, which is the URL from which the
manifest was fetched. This algorithm will return a list of
icons objects icons, which can be empty.
icons
".
false
.
src
member of an icon
with potential icon and manifest URL.
undefined
, move onto
the next item in icons (if any are left).
src
, type
,
sizes
, and density
. All properties
initially set to undefined
.
src
property to be
src.
type
member of an icon
passing potential icon.
undefined
, set
icon's type
property to be
type.
sizes
member of an
icon passing potential icon.
undefined
, set
icon's sizes
property to be
sizes.
density
member of an
icon are given by the passing potential
icon.
undefined
, set
icon's density
property to be
value.
undefined
:
If there are multiple equally appropriate icons in icons, a user agent MUST use the last one declared in order at the time that the user agent collected the list of icons. If the user agent tries to use an icon but that icon is determined, upon closer examination, to in fact be inappropriate (e.g. because its content type is unsupported), then the user agent MUST try the next-most-appropriate icon as determined by examining the icon object's members.
display
member
The display
member is a
string, whose value is one of display
modes values. The item represents the developer's preferred
display mode for the web application. When the member is
missing or erroneous, the user agent MUST use the fallback display
mode.
The steps for processing the display
member
are given by the following algorithm. The algorithm takes a manifest
manifest as an argument, and returns a string.
display
" as the argument.
orientation
member
The orientation
member is a string that serves as the
default orientation for all top-level browsing contexts of the
web application. The possible values is one of the
OrientationLockType
enum defined in
[SCREEN-ORIENTATION].
If the user agent honors the value of the orientation
member as the default orientation, then that serves as the
default orientation for the life of the web application
(unless overridden by some other means at runtime). This means that
the user agent MUST return the orientation to the default
orientation any time the orientation is unlocked
[SCREEN-ORIENTATION] or the top-level browsing context is
navigated.
Although the specification relies on the [SCREEN-ORIENTATION]'s
OrientationLockType
, it is OPTIONAL for a user
agent to implement the [SCREEN-ORIENTATION] API. Supporting the
[SCREEN-ORIENTATION] API is, of course, RECOMMENDED.
Certain UI/UX concerns and/or platform conventions will mean that
some screen orientations and display modes cannot be used
together. Which orientations and display modes cannot be used
together is left to the discretion of implementers. For example, for
some user agents, it might not make sense to change the default
orientation of an application while in browser
display mode.
Once the web application is running, other means can change the orientation of a top-level browsing context (such as via [SCREEN-ORIENTATION] API).
The steps for processing the orientation
member are given by the following algorithm. The algorithm
takes a manifest manifest and display mode
display mode as an argument, and returns a string.
orientation
".
OrientationLockType
enum values, or
value is unsupported by the user agent, or the
value cannot be used together with display
mode:
start_url
member
The start_url
member is a
string that represents the start
URL, which is URL that the developer would prefer the
user agent load when the user launches the web application (e.g.,
when the user clicks on the icon of the web application from a
device's application menu or homescreen).
The start_url
member is purely
advisory, and a user agent MAY ignore it or provide the
end-user the choice not to make use of it. A user agent MAY also
allow the end-user to modify the URL when, for instance, a bookmark
for the web application is being create or any time thereafter.
The steps for processing the start_url
member
are given by the following algorithm. The algorithm takes a
manifest manifest, a URL manifest
URL, and a URL document URL. This algorithm
returns a URL.
start_url
".
undefined
", issue
a developer warning that the type is unsupported.
start_url
needs to be same-origin as
Document
of the top-level browsing context.
For example, if the value of start_url
is
../start_point.html, and the manifest's URL is
https://example.com/resources/manifest.json, then the
result of URL parsing would be
https://example.com/start_point.html.
Each icon object represents an icon for a web application, suitable to use in various contexts (e.g., an application menu). As icons are usually images, this specification provides developers with a means of specifying the dimensions, optimal pixel density, and media type of an icon. A user agent can use these values to select an icon that is best suited to display on the end-user's device or most closely matches the end-user's preferences.
In the following example, the developer has made the following choices about the icons of the web application:
type
member. If the user agent doesn't support WebP, it
falls back to the second icon of the same size (and density). The
media type of this icon can then be either determined via a HTTP
header, or can be sniffed by the user agent once the first few bytes
of the icon are received.
{ "icons": [ { "src": "icon/lowres.webp", "sizes": "48x48", "type": "image/webp" },{ "src": "icon/lowres", "sizes": "48x48" },{ "src": "icon/hd_hi.ico", "sizes": "72x72 96x96 128x128 256x256" },{ "src": "icon/hd_hi.svg", "sizes": "72x72", "density": 2 }] }
For all intents and purposes, an icon object is functionally
equivalent to link
element whose
rel
attribute is icon in a Document
.
The security policy that governs whether a user agent can
fetch an icon image is governed by the image-src
directive [CSP2] associated with the manifest's owner
Document
.
For example, the following policy restricts loading icons the
icons.example.com
domain. Thus, trying to load icons
from "other.com" would fail.
HTTP/1.1 200 OK Content-Type: application/json Content-Security-Policy: img-src icons.example.com; { "name": "custom manifest", "start_url": "http://boo", "icons": [{ "src": "//icons.example.com/lowres" }, { "src": "//other.com/hi-res" }] }
density
member
The density member of an icon is the
device pixel density for which this icon was designed. The device
pixel density is expressed as the number of dots per 'px' unit
(equivalent to a dppx as defined in [css3-values]). The value is a
positive number greater than 0. If the developer omits the value, the
user agent assumes the value 1.0
.
The steps for processing a density
member of an
icon are given by the following algorithm. The algorithm thanks
an icon object as an argument and returns a positive
number.
density
as the argument returns false
:
density
" as the argument.
NaN
, +∞, or less than or
equal to +0, then:
sizes
member
The sizes member is a string consisting of an unordered set of unique space-separated tokens which are ASCII case-insensitive that represents the dimensions of an icon for visual media. Each keyword is either an ASCII case-insensitive match for the string "any", or a value that consists of two valid non-negative integers that do not have a leading U+0030 DIGIT ZERO (0) character and that are separated by a single U+0078 LATIN SMALL LETTER X or U+0058 LATIN CAPITAL LETTER X character. The keywords represent icon sizes in raw pixels (as opposed to CSS pixels). When multiple icon objects are available, a user agent can use the value to decide which icon is most suitable for a display context (and ignore any that are inappropriate).
The steps for processing a sizes
member of an
icon are given by the following algorithm. The algorithm takes
an icon object icon. This algorithm will return a
set.
sizes
" as the argument.
undefined
", issue
a developer warning that the type is unsupported.
sizes
attribute and let keywords be the
result.
src
member
The src member of an icon is a URL from which a user agent can fetch the icon's data.
The steps for processing the src
member of an
icon are given by the following algorithm. The algorithm takes
a icon object icon, and a URL manifest
URL, which is the URL from which the manifest
was fetched. This algorithm will return a URL or
undefined
.
src
" as the argument.
undefined
", issue a
developer warning that the type is unsupported.
undefined
.
undefined
.
type
member
The type member of an icon is a hint as to the media type of the icon. The purpose of this member is to allow a user agent to ignore icons of media types it does not support.
There is no default MIME type for icon objects. However, for the purposes of determining the type of the resource, user agents must expect the resource to be an image.
The steps for processing the type
member of an
icon are given by the following algorithm. The algorithm takes
an icon object as an argument, and returns either a string
or undefined
.
type
" as the argument.
undefined
", issue a
developer warning that the type is unsupported.
undefined
.
undefined
.
The [[GetOwnProperty]] operation and the abstract operation hasOwnProperty, parseFloat(string) function, and the Type(x) notation are defined in [ECMASCRIPT].
When instructed to Trim(x), a user agent MUST behave as if [ECMASCRIPT]'s String.prototype.trim() function had been called on the string x.
As the manifest uses the JSON format, this specification relies on the
types defined in [ECMA-404] specification: namely object, array,
number, string, true
, false
, and
null
. Strict type checking is not enforced by this
specification. Instead, each member's definition specifies the steps
required to process a particular member and what to do when a type does
not match what is expected.
The URL concept and URL parsing are defined in [WHATWG-URL].
The
default orientation concept and the
OrientationLockType
enum, are defined in
[SCREEN-ORIENTATION].
The following are defined in [HTML]:
link
element
rel
attribute
a
element
meta
element
area
element
name
attribute
title
element
The following registration is for community review and will be submitted to the IESG for review, approval, and registration with IANA.
This section contains the required text for MIME media type registration with IANA.
The media type for a manifest is
application/manifest+json
.
If the protocol over which the manifest is transferred supports the [MIME-TYPES] specification (e.g. HTTP), it is RECOMMENDED that the manifest be labeled with the media type for a manifest.
This specification does not directly deal with high-value data. However, installed web applications and their data could be seen as "high value" (particulaly from a privacy perspective).
As the manifest format is JSON and will commonly be encoded using [UNICODE], the security considerations described in [ECMA-404] and [UNICODE-SECURITY] apply. In addition, because there is no way to prevent developers from including custom/unrestrained data in a manifest, implementors need to impose their own implementation-specific limits on the values of otherwise unconstrained member types, e.g. to prevent denial of service attacks, to guard against running out of memory, or to work around platform-specific limitations.
Web applications will generally contain ECMAScript, HTML, CSS files, and other media, which are executed in a sand-boxed environment. As such, implementors need to be aware of the security implications for the types they support. Specifically, implementors need to consider the security implications outlined in at least the following specifications: [CSS-MIME], [ECMAScript-MIME], [HTML].
As web applications can contain content that is able to simultaneously interact with the local device and a remote host, implementors need to consider the privacy implications resulting from exposing private information to a remote host. Mitigation and in-depth defensive measures are an implementation responsibility and not prescribed by this specification. However, in designing these measures, implementors are advised to enable user awareness of information sharing, and to provide easy access to interfaces that enable revocation of permissions.
As this specification allows for the declaration of URLs within certain members of a manifest, implementors need to consider the security considerations discussed in the [WHATWG-URL] specification. Implementations intending to display IRIs and IDNA addresses found in the manifest are strongly encouraged to follow the security advice given in [UNICODE-SECURITY].
Developers need to be aware of the security considerations
discussed throughout the [CSP2] specification, particularly in
relation to making data:
a valid source for the
purpose of inlining
a manifest. Doing so can enable XSS
attacks by allowing a manifest to be included directly in the
document itself; this is best avoided completely.
As well as sections marked as non-normative, all authoring guidelines, diagrams, examples, and notes in this specification are non-normative. Everything else in this specification is normative.
The key words MAY, MUST, MUST NOT, OPTIONAL, RECOMMENDED, and REQUIRED are to be interpreted as described in [RFC2119].
There is only one class of product that can claim conformance to this specification: a user agent.
This section is non-normative.
This specification is designed to be extensible. Other specifications are encouraged to define new members for the manifest. However, in doing so, please follow the conventions used in this specification. In particular, use the extension point to hook into the steps for processing a manifest. Also, be sure to specify the steps for processing your particular member in the manner set forth in this specification. This will help keep this part of the platform consistent.
When specifying a new member, don't override or monkey patch anything defined in this specification. Also, don't assume your member will be processed before or after any other member. Keep your new member, and its processing, atomic and self contained. Note also that implementations are free to ignore any member they do not recognize or support.
If you are writing a specification and temporarily want to patch this specification to help implementations along, file a bug so the community is informed of what you are trying to do.
This section is non-normative.
Although proprietary extensions are undesirable, they can't realistically be avoided. As such, the RECOMMENDED way to add a new proprietary manifest member as an extension is to use a vendor prefix.
The following is an example of two hypothetical vendor extensions.
{ ... "webkit_fancy_feature": "some/url/img", "moz_awesome_thing": { ... } ... }
The mechanisms defined by the [JSON-LD] specification can be used as an alternative mechanism for extending the manifest.
In the following example, for instance, elements from both the Dublin Core Metadata Set [DC-TERMS], the Friend of a Friend [FOAF] vocabulary, and the Description of a Project (DOAP) vocabulary are used to provide additional information in the manifest:
{ "@context": { "@vocab": "http://www.w3.org/TR/appmanifest/", "foaf": "http://xmlns.com/foaf/0.1/", "dct": "http://purl.org/dc/terms/", "doap": "http://usefulinc.com/ns/doap#" }, "name": "Super Racer 2000", "dct:creator": "http://example.com", "dct:abstract": "A Super Racer Game!", "doap:maintainer": { "foaf:name": "Joe" }, "icons": [{ "src": "icon/lowres", "sizes": "64x64", "type": "image/webp" }, { "src": "icon/hd_small", "sizes": "64x64" }, { "src": "icon/hd_hi", "sizes": "128x128" }], "start_url": "/start.html", "display": "fullscreen", "orientation": "landscape" }
Non JSON-LD implementations can simply ignore the additional JSON-LD
specific metadata such as @context
and the extension
properties dct:creator
, dct:abstract
and
doap:maintainer
.
For implementations that do process the manifest as JSON-LD, the
manifest's own property names are interpreted relative to the base URI
"http://www.w3.org/TR/appmanifest/
".
After processing the example above, a JSON-LD implementation would yield the following normalized output:
_:c14n0 <http://www.w3.org/TR/appmanifest/sizes> "64x64" . _:c14n0 <http://www.w3.org/TR/appmanifest/src> "icon/hd_small" . _:c14n1 <http://purl.org/dc/terms/abstract> "A Super Racer Game!" . _:c14n1 <http://purl.org/dc/terms/creator> "http://example.com" . _:c14n1 <http://usefulinc.com/ns/doap#maintainer> _:c14n4 . _:c14n1 <http://www.w3.org/TR/appmanifest/display> "fullscreen" . _:c14n1 <http://www.w3.org/TR/appmanifest/icons> _:c14n0 . _:c14n1 <http://www.w3.org/TR/appmanifest/icons> _:c14n2 . _:c14n1 <http://www.w3.org/TR/appmanifest/icons> _:c14n3 . _:c14n1 <http://www.w3.org/TR/appmanifest/name> "Super Racer 2000" . _:c14n1 <http://www.w3.org/TR/appmanifest/orientation> "landscape" . _:c14n1 <http://www.w3.org/TR/appmanifest/start_url> "/start.html" . _:c14n2 <http://www.w3.org/TR/appmanifest/sizes> "64x64" . _:c14n2 <http://www.w3.org/TR/appmanifest/src> "icon/lowres" . _:c14n2 <http://www.w3.org/TR/appmanifest/type> "image/webp" . _:c14n3 <http://www.w3.org/TR/appmanifest/sizes> "128x128" . _:c14n3 <http://www.w3.org/TR/appmanifest/src> "icon/hd_hi" . _:c14n4 <http://xmlns.com/foaf/0.1/name> "Joe" .
link
and meta
elements
An extensive discussion of why we chose to use JSON instead of HTML
meta
/link
tags for this specification is
available on GitHub and on the
www-tag
list. Below is a short summary of the key points raised in those
discussions.
The document format defined in this specification provides a unified
means of encapsulating metadata about a Web application in a way that
we hope will avoid existing pitfalls with both proprietary and
[HTML]'s meta
/link
tags. Those pitfalls
include:
Although it would be unrealistic to think that this specification won't bring its own set of problems, externalizing this data in the form of a manifest solves the problems described above. These problems are solved by:
meta
tags are currently using, especially when a tag's
value contains several sub-values.
In addition, standardizing the functionality currently provided by the
various meta
tag-based solutions within the manifest
solves the problem of having to declare large number of proprietary and
standard [HTML] tags that all achieve the same thing. Of course,
this hinges on the standard actually getting implemented by browsers
and those browsers getting widely deployed to users: if this happens,
the Web community might be able to retire many of the proprietary
meta
tags plaguing the Web at the time of writing. More
information about the proprietary tags can be found in the
Use
Cases and Requirements for Installable Web Apps.
Lastly, this specification does not make the standardized solutions
found in [HTML] redundant. When members like the name
or icons
is missing from the manifest, user agents can
search in a manifest's owner [HTML] document for things like icons
and the application name (or a user agent might even fallback to
proprietary tags/metadata, if they are present in a document).
Developers interested in validating manifest documents can find an unofficial JSON schema for the manifest format at schemastore.org. It is licensed under Apache 2.0. It is kindly maintained by Mads Kristensen. If you find any issues with the JSON schema, please file a bug at the SchemaStore repository on GitHub.
This document reuses text from the [HTML] specification, edited by Ian Hickson, as permitted by the license of that specification.