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<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>
Web Application Manifest
</title>
<script src="https://www.w3.org/Tools/respec/respec-w3c" class=
"remove"></script>
<script class='remove'>
var respecConfig = {
mdn: true,
previousPublishDate: "2013-12-17",
specStatus: "ED",
shortName: "appmanifest",
prevVersion: "FPWD",
previousMaturity: "WD",
formerEditors: [
{
name: "Matt Giuca",
company: "Google Inc.",
companyURL: "https://www.google.com/",
w3cid: 91260,
retiredDate: "2024-07-01",
},
{
name: "Anssi Kostiainen",
company: "Intel Corporation",
companyURL: "https://intel.com/",
w3cid: 41974,
retiredDate: "2024-05-10",
},
{
name: "Aaron Gustafson",
company: "Microsoft Corporation",
companyURL: "https://microsoft.com/",
w3cid: 43672,
retiredDate: "2024-05-10",
},
{
name: "Mounir Lamouri",
company: "Google Inc.",
companyURL: "https://www.google.com/",
},
{
name: "Rob Dolin",
company: "Microsoft Corporation",
companyURL: "https://www.microsoft.com/",
},
],
editors: [
{
name: "Marcos Cáceres",
company: "Apple",
companyURL: "https://apple.com",
w3cid: 39125,
},
{
name: "Kenneth Rohde Christiansen",
company: "Intel Corporation",
companyURL: "https://intel.com/",
w3cid: 57705,
},
{
name: "Diego González",
company: "Microsoft Corporation",
companyURL: "https://microsoft.com/",
w3cid: 66757,
},
{
name: "Daniel Murphy",
company: "Google Inc.",
companyURL: "https://www.google.com/",
w3cid: 90918,
},
{
name: "Christian Liebel",
company: "Thinktecture AG",
companyURL: "https://www.thinktecture.com/",
w3cid: 109589,
},
],
group: "webapps",
github: "https://github.com/w3c/manifest/",
caniuse: {
versions: 1,
feature: "web-app-manifest",
browsers: [
"chrome",
"and_chr",
"edge",
"and_ff",
"ios_saf",
],
},
xref: "web-platform",
};
</script>
<style>
.icon-title {
text-transform: uppercase;
font-weight: bold;
}
.icons {
display: flex;
flex-direction: row;
flex-wrap: wrap;
}
.icons > figure {
text-align: left;
margin: 0;
padding: 10px;
width: 188px;
}
.icons > figure > img {
width: 188px;
height: 188px;
min-width: 188px;
min-height: 188px;
}
.icons > figure .icon-title {
display: block;
}
</style>
</head>
<body data-cite=
"ENCODING SCREEN-ORIENTATION MEDIAQUERIES-5 IMAGE-RESOURCE MIMESNIFF">
<section id='abstract'>
<p>
This specification defines a JSON-based file format that provides
developers with a centralized place to put metadata associated with a
web application. This metadata 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 screen 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 manifest is applied and provides a
means to "deep link" into a web application from other applications.
</p>
<p>
Using this metadata, user agents can provide developers with means to
create user experiences that are more comparable to that of a native
application.
</p>
</section>
<section id="sotd">
<aside class="warning">
<p>
Implementors need to be aware that this specification is not stable.
However, aspects of this specification are shipping in at least one
browser (see links to implementation status at the top of this
document). <strong>Implementors who are not taking part in the
discussions will find the specification changing out from under them
in incompatible ways.</strong> Vendors interested in implementing
this specification before it eventually reaches the Candidate
Recommendation phase should <a href=
"https://github.com/w3c/manifest/issues">subscribe to the repository
on GitHub</a> and take part in the discussions.
</p>
</aside>
</section>
<section>
<h2>
Web Application Manifest
</h2>
<p>
An <dfn data-export="" data-lt="manifest" data-local-lt=
"manifest's">application manifest</dfn> is a [[JSON]] document that
contains startup parameters and application defaults for when a web
application is launched.
</p>
<p>
A manifest has an associated <dfn class="export">manifest URL</dfn>,
which is the [[URL]] from which the <a>manifest</a> was fetched.
</p>
<p>
A [=manifest=] can have any of the following members at its root, all
of which are optional. The members can appear in any order.
</p>
<ul>
<li>[=manifest/background_color=]
</li>
<li>[=manifest/dir=]
</li>
<li>[=manifest/display=]
</li>
<li>[=manifest/icons=]
</li>
<li>[=manifest/identity=]
</li>
<li>[=manifest/lang=]
</li>
<li>[=manifest/name=]
</li>
<li>[=manifest/orientation=]
</li>
<li>[=manifest/scope=]
</li>
<li>[=manifest/short_name=]
</li>
<li>[=manifest/shortcuts=]
</li>
<li>[=manifest/start_url=]
</li>
<li>[=manifest/theme_color=]
</li>
</ul>
<aside class="note">
<p>
Although it is optional for any member to appear in a manifest, some
user agents might require one or more to be present to take full
advantage of the capabilities afforded by this specification.
</p>
</aside>
<section class="informative">
<h3>
Examples
</h3>
<p>
This section shows how developers can make use of the various
features of this specification.
</p>
<section class="informative">
<h3>
Typical structure
</h3>
<p>
The following shows a typical <a>manifest</a>.
</p>
<pre class="example json" title="Typical manifest">
{
"lang": "en",
"dir": "ltr",
"name": "Super Racer 3000",
"short_name": "Racer3K",
"icons": [{
"src": "icon/lowres.webp",
"sizes": "64x64",
"type": "image/webp"
}, {
"src": "icon/lowres.png",
"sizes": "64x64"
}, {
"src": "icon/hd_hi",
"sizes": "128x128"
}],
"scope": "/",
"id": "superracer",
"start_url": "/start.html",
"display": "fullscreen",
"orientation": "landscape",
"theme_color": "aliceblue",
"background_color": "red"
}
</pre>
</section>
<section class="informative">
<h3>
Using a `link` element to link to a manifest
</h3>
<p>
The example also shows how to use the link type "manifest" and how
to use other [^meta^] and [^link^] elements to give the web
application a fallback name and set of icons.
</p>
<pre class="example html" title="Linking to a manifest">
<!doctype>
<html>
<title>Racer 3K</title>
<!-- Startup configuration -->
<link rel="manifest" href="manifest.webmanifest">
<!-- Fallback application metadata for legacy browsers -->
<meta name="application-name" content="Racer3K">
<link rel="icon" sizes="16x16 32x32 48x48" href="lo_def.ico">
<link rel="icon" sizes="512x512" href="hi_def.png">
</pre>
<aside class="note" title="File extension: .webmanifest or .json?">
The IANA <a href=
"https://www.iana.org/assignments/media-types/application/manifest+json">
registered</a> file extension for the manifest is `.webmanifest`.
Some web servers recognize this extension and transfer the file
using the standardized <a>application manifest media type</a>
([=application\/manifest+json=]). Developers can also choose a
different extension (e.g. `.json`) or none at all (e.g.
`/api/GetManifest`), but are encouraged to transfer the manifest
using the [=application\/manifest+json=] [=MIME type=], although
any [=JSON MIME type=] is ok.
</aside>
</section>
<section class="informative">
<h3>
Declaring multiple icons
</h3>
<p>
In the following example, the developer has made the following
choices about the icons associated with the web application:
</p>
<ul>
<li>The developer has included two icons at the same size, but in
two different formats. One is explicitly marked as WebP through the
`type` member. If the user agent doesn't support WebP, it falls
back to the second icon of the same size. The <a>MIME type</a> of
this icon can then be either determined via a HTTP header, or can
be <a data-lt="computed mime type">sniffed</a> by the user agent
once the first few bytes of the icon are received.
</li>
<li>The developer wants to use an SVG for greater than or equal to
257x257px. They've found that the SVG file looks too blurry at
small sizes, even on high-density screens. To deal with this
problem, the developer includes an SVG icon that is only used when
the dimensions are at least 257px. Otherwise, the user agent uses
the ICO file (hd_hi.ico), which includes a gamut of raster icons
individually tailored for small display sizes.
</li>
</ul>
<pre class="example json" title="Multiple icons">
{
"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": "257x257"
}]
}
</pre>
</section>
<section class="informative">
<h3>
Creating shortcuts
</h3>
<p>
In the following example, the developer has included two shortcuts.
Assuming the manifest's URL is
<samp>https://example.com/manifest.webmanifest</samp>:
</p>
<ul>
<li>The first shortcut would be displayed with the text "Play
Later". If the operating system supports icons for context menu
items and it also supports SVG images for that purpose, the user
agent would present
<samp>https://example.com/icons/play-later.svg</samp> next to the
text. When launched, the user agent would instantiate a new
<a>top-level browsing context</a> and navigate to
<samp>https://example.com/play-later</samp>.
</li>
<li>The second shortcut would be displayed with the text
"Subscriptions". When launched, the user agent would instantiate a
new <a>top-level browsing context</a> and navigate to
<samp>https://example.com/subscriptions?sort=desc</samp>.
</li>
</ul>
<pre class="example json" title="Adding shortcuts">
{
"shortcuts": [
{
"name": "Play Later",
"description": "View the list of podcasts you saved for later",
"url": "/play-later",
"icons": [
{
"src": "/icons/play-later.svg",
"type": "image/svg+xml"
}
]
},
{
"name": "Subscriptions",
"description": "View the list of podcasts you listen to",
"url": "/subscriptions?sort=desc"
}
]
}
</pre>
</section>
<section class="informative">
<h2>
Understanding "scope"
</h2>
<p>
The [=manifest/scope=] member tells the browser which documents are
part of a web application, and which are not - and hence, to which
set of web pages the manifest is "[=applied=]" when the user
navigates around a web site.
</p>
<p>
For example, `{"scope": "/"}` means that the manifest applies to
every document in an origin. On the other hand, `{"scope":
"/racer/"}` means that only documents within the path "/racer/" are
[=URL/within scope=]: so "/racer/race1.html", "/racer/race2.html",
etc. would all be [=URL/within scope=], but "/elsewhere/" and
anything at the root "/" would be "out of scope" and the manifest
wouldn't apply to documents in those paths. Only one scope path is
supported. See [[[#nav-scope]]] for the technical details.
</p>
<p>
[=Applying=] a manifest means that any members that affect
presentation found in the manifest will come into effect, such as
display "fullscreen", or applying a particular screen orientation.
As long as the application is navigated to URLs that are
[=URL/within scope=], the browser will continue to apply the
manifest. However, navigating the web applications "out of scope"
will cause the manifest to no longer be applied, and the browser
will apply its own defaults. This will cause, for example, the
application to no longer be displayed in fullscreen, and instead be
displayed as a regular web page in a browser tab. It's left up to
implementers to decide how to deal with web pages being navigated
in and out of scope. See [[[#applying]]] for the technical details.
</p>
<p>
Finally, as it's possible that a user can install a web application
from any document within an origin, it's good practice to always
declare a [=manifest/scope=] member in a manifest. If the
[=manifest/scope=] member is missing from the manifest, then the
path of the [=manifest/start_url=] member is used as a fallback.
And if the [=manifest/start_url=] member is also missing, then the
document URL from which the web application is installed gets used
as the scope. To be sure you don't get any unexpected navigation
behavior, always include a [=manifest/scope=] member preferably set
to `"/"`.
</p>
</section>
</section>
<section>
<h3>
`dir` member
</h3>
<p>
The [=manifest's=] <code><dfn data-export="" data-dfn-for=
"manifest">dir</dfn></code> member specifies the <dfn>default
direction</dfn> for the [=localizable members=] of the [=manifest=].
The [=manifest/dir=] member's value can be set to a
[=text-direction=].
</p>
<p>
The <dfn>text-directions</dfn> are the following, implying that the
value of the [=localizable members=] is by default:
</p>
<dl>
<dt>
"<dfn data-dfn-for="text-direction">ltr</dfn>"
</dt>
<dd>
Left-to-right text.
</dd>
<dt>
"<dfn data-dfn-for="text-direction">rtl</dfn>"
</dt>
<dd>
Right-to-left text.
</dd>
<dt>
"<dfn data-dfn-for="text-direction">auto</dfn>" (default)
</dt>
<dd>
Text direction is unknown. The user agent should use heuristics to
estimate the display of the text, for example the first-strong
algorithm as described in [[UAX9]].
</dd>
</dl>
<p>
The <dfn>text-direction list</dfn> is the [=list=] «
"[=text-direction/ltr=]", "[=text-direction/rtl=]",
"[=text-direction/auto=]" ».
</p>
<p>
To <dfn>process the `dir` member</dfn>, given [=ordered map=]
|json:ordered map| and [=ordered map=] |manifest:ordered map|:
</p>
<ol class="algorithm">
<li>Set |manifest|["dir"] to "auto".
</li>
<li>If |json|["dir"] doesn't [=map/exist=] or if |json|["dir"] is not
a [=string=], return.
</li>
<li>[=Strip leading and trailing ASCII whitespace=] from
|json|["dir"].
</li>
<li>[=ASCII lowercase=] |json|["dir"].
</li>
<li>If [=text-direction list=] doesn't [=list/contain=]
|json|["dir"], return.
</li>
<li>Set |manifest|["dir"] to |json|["dir"].
</li>
</ol>
</section>
<section>
<h3>
`lang` member
</h3>
<p>
The [=manifest's=] <code><dfn data-export="" data-dfn-for=
"manifest">lang</dfn></code> member is a [=string=] in the form of a
[=language tag=] that specifies the language for the values of the
manifest's [=localizable members=]. If the `lang` member is not
specified, the language is treated as unknown.
</p>
<p class="note">
Specifying the language improves the user experience by helping user
agents select the most appropriate processing or resources, such as
fonts, styling, hyphenation, or text-to-speech voices for
accessibility.
</p>
<p>
A <dfn>language tag</dfn> is a [=string=] that matches the production
of a well-formed `Language-Tag` defined in [[BCP47]].
</p>
<p class="note">
Language tags are case-insensitive. Examples of language tags include
'`fr`' (French), '`en-AU`' (English as spoken in Australia), or
'`zh-Hans-CN`' (Chinese as written in the Simplified Han script as
spoken in China).
</p>
<p>
To <dfn>process the `lang` member</dfn>, given [=ordered map=]
|json:ordered map| and [=ordered map=] |manifest:ordered map|:
</p>
<ol class="algorithm">
<li>If |json|["lang"] doesn't [=map/exist=] or if |json|["lang"] is
not a [=string=], return.
</li>
<li>[=Strip leading and trailing ASCII whitespace=] from
|json|["lang"].
</li>
<li>If calling <a data-cite=
"ECMA-402#sec-isstructurallyvalidlanguagetag">IsStructurallyValidLanguageTag</a>
with |json|["lang"] returns `false`, return.
</li>
<li>[=Map/Set=] |manifest|["lang"] to the result of calling the
<a data-cite=
"ECMA-402#sec-canonicalizeunicodelocaleid">CanonicalizeUnicodeLocaleId</a>
abstract operation with |json|["lang"].
</li>
</ol>
</section>
<section>
<h3>
`name` member
</h3>
<p>
The [=manifest's=] <code><dfn data-export="" data-dfn-for=
"manifest">name</dfn></code> member is a <a>string</a> 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).
</p>
<p>
The [=manifest/name=] member is a [=localizable member=].
</p>
<p>
The [=manifest/name=] member serves as the <a data-cite=
"accname-1.2#dfn-accessible-name">accessible name</a> of an
[=installed web application=].
</p>
<p class="note" title="Processing the `name` member">
When [=processing a manifest=], the [=process a text member=]
algorithm is used to process the [=manifest/name=] member.
</p>
</section>
<section>
<h3>
`short_name` member
</h3>
<p>
The [=manifest's=] <code><dfn data-export="" data-dfn-for=
"manifest">short_name</dfn></code> member is a <a>string</a> 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.
</p>
<p>
The [=manifest/short_name=] member is a [=localizable member=].
</p>
<p class="note" title="Processing the `short_name` member">
When [=processing a manifest=], the [=process a text member=]
algorithm is used to process the [=manifest/short_name=] member.
</p>
</section>
<section>
<h3>
`scope` member
</h3>
<p>
The [=manifest's=] <code><dfn data-export="" data-dfn-for=
"manifest">scope</dfn></code> member is a <a>string</a> that
represents the [=manifest/navigation scope=] of this web
application's <a>application context</a>.
</p>
<aside class="note" title="Default scope">
<p>
The "default scope" (when [=manifest/scope=] member is missing,
empty, or failure) is the [=start URL=], but with its filename,
query, and fragment removed.
</p>
</aside>
<p>
To <dfn>process the `scope` member</dfn>, given [=ordered map=]
|json:ordered map| and [=ordered map=] |manifest:ordered map|:
</p>
<ol class="algorithm">
<li>Set |manifest|["scope"] to the result of [=URL Parser|parsing=]
"." with |manifest|["start_url"] as the base URL.
</li>
<li>If |json|["scope"] is the empty string, then return.
</li>
<li>Let |scope:URL| be the result of [=URL Parser|parsing=]
|json|["scope"] with |manifest URL| as the base URL.
</li>
<li>If |scope| is failure, return.
</li>
<li>Set |scope|'s [=URL/query=] and [=URL/fragment=] to null.
</li>
<li>If |manifest|["start_url"] is not [=URL/within scope=] of
|scope|, return.
</li>
<li>Otherwise, set |manifest|["scope"] to |scope|.
</li>
</ol>
</section>
<section>
<h3>
`icons` member
</h3>
<p>
The [=manifest's=] <code><dfn data-export="" data-dfn-for=
"manifest">icons</dfn></code> member are images that 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 <abbr title="Operating system">OS</abbr>'s task switcher and/or
system preferences.
</p>
<p>
The [=manifest/icons=] member is a [=localizable member=].
</p>
<aside class="note">
<p>
When [=processing a manifest=], the [=process image resources=]
algorithm is used to process the [=manifest/icons=] member.
</p>
</aside>
</section>
<section>
<h3>
`display` member
</h3>
<p>
The [=manifest's=] <code><dfn data-export="" data-dfn-for=
"manifest">display</dfn></code> member represents the developer's
preferred <a>display mode</a> for the web application. Its value is a
[=display mode=].
</p>
<p>
To <dfn>process the `display` member</dfn>, given [=ordered map=]
|json:ordered map| and [=ordered map=] |manifest:ordered map|:
</p>
<ol class="algorithm">
<li>Set |manifest|["display"] to "browser".
</li>
<li>If |json|["display"] doesn't [=map/exist=] or |json|["display"]
is not a a [=string=], return.
</li>
<li>[=Strip leading and trailing ASCII whitespace=] from
|json|["display"].
</li>
<li>[=ASCII lowercase=] |json|["display"].
</li>
<li>If [=display modes list=] doesn't [=list/contain=]
|json|["display"], return.
</li>
<li>Set |manifest|["display"] to |json|["display"].
</li>
</ol>
</section>
<section>
<h3>
`orientation` member
</h3>
<p>
The [=manifest's=] <code><dfn data-export="" data-dfn-for=
"manifest">orientation</dfn></code> member is a <a>string</a> that
serves as the <a>default screen orientation</a> for all <a>top-level
browsing contexts</a> of the web application. The possible values are
those of the {{OrientationLockType}} enum, which in this
specification are referred to as the <dfn>orientation values</dfn>
(i.e., "any", "natural", "landscape", "portrait", "portrait-primary",
"portrait-secondary", "landscape-primary", or "landscape-secondary").
</p>
<p>
If the user agent supports the value of the [=manifest/orientation=]
member as the <a>default screen orientation</a>, then that serves as
the <a>default screen orientation</a> 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
<a>default screen orientation</a> any time the orientation is
unlocked [[SCREEN-ORIENTATION]] or the <a>top-level browsing
context</a> is <a>navigated</a>.
</p>
<p class="note">
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, encouraged.
</p>
<p>
Certain UI/UX concerns and/or platform conventions will mean that
some screen orientations and <dfn>cannot be used together</dfn>.
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 <a>default screen
orientation</a> of an application while in `browser` <a>display
mode</a>.
</p>
<p class="note">
Once the web application is running, other means can change the
orientation of a <a>top-level browsing context</a> (such as via
[[SCREEN-ORIENTATION]] API).
</p>
<p>
To <dfn>process the `orientation` member</dfn>, given [=ordered map=]
|json:ordered map| and [=ordered map=] |manifest:ordered map|:
</p>
<ol class="algorithm">
<li>If |json|["orientation"] doesn't [=map/exist=] or
|json|["orientation"] is not a [=string=], return.
</li>
<li>[=Strip leading and trailing ASCII whitespace=] from
|json|["orientation"].
</li>
<li>[=ASCII lowercase=] |json|["orientation"].
</li>
<li>If |json|["orientation"] doesn't [=list/contain=] any of the
[=orientation values=], return.
</li>
<li>Set |manifest|["orientation"] to |json|["orientation"].
</li>
</ol>
</section>
<section>
<h3>
`start_url` member
</h3>
<p>
The [=manifest's=] <code><dfn data-export="" data-dfn-for=
"manifest">start_url</dfn></code> member is a <a>string</a> that
represents the <dfn class="export">start URL</dfn> , which is
<a>URL</a> 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).
</p>
<p>
The [=manifest/start_url=] member is purely advisory, and a user
agent MAY <a>ignore</a> 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 created or any time thereafter.
</p>
<p>
To <dfn>process the `start_url` member</dfn>, given [=ordered map=]
|json:ordered map|, [=ordered map=] |manifest:ordered map|, [=URL=]
|manifest URL:URL|, and [=URL=] |document URL:URL|:
</p>
<ol class="algorithm">
<li>Set |manifest|["start_url"] to |document URL|.
</li>
<li>If |json|["start_url"] doesn't [=map/exist=] or
|json|["start_url"] is not a [=string=], return.
</li>
<li>If the type of |json|["start_url"] is not [=string=], or if
|json|["start_url"] is the empty string, return.
</li>
<li>Let |start URL:URL| be the result of [=URL Parser|parsing=]
|json|["start_url"], using |manifest URL| as the base URL.
</li>
<li>If |start URL| is failure, return.
</li>
<li>If |start URL| is not <a>same origin</a> as |document URL|,
return.
</li>
<li>Otherwise, set |manifest|["start_url"] to |start URL|.
</li>
</ol>
<aside class="example">
<p>
For example, if the value of [=manifest/start_url=] is
<samp>../start_point.html</samp>, and the manifest's URL is
<samp>https://example.com/resources/manifest.webmanifest</samp>,
then the result of [=URL parser|parsing=] would be
<samp>https://example.com/start_point.html</samp>.
</p>
</aside>
<section>
<h3>
Privacy consideration: [=manifest/start_url=] tracking
</h3>
<p>
It's conceivable that the [=manifest/start_url=] could be crafted
to indicate that the application was launched from outside the
browser (e.g., `"start_url": "index.html?launcher=homescreen"`).
This can be useful for analytics and possibly other customizations.
However, it is also conceivable that developers could encode
strings into the start_url that uniquely identify the user (e.g., a
server-assigned identifier, such as `"?user=123"`, `"/user/123/"`,
or `"https://user123.foo.bar"`). This is fingerprinting/privacy
sensitive information that the user might not be aware of.
</p>
<p class="note" title="Don't add identifiers to start URLs">
It is bad practice for a developer to use the [=start URL=] to
include information that uniquely identifies a user, as it would
represent a fingerprint that is not cleared when the user clears
site data. However, nothing in this specification can practically
prevent developers from doing this.
</p>
<p>
Given the above, it is RECOMMENDED that, upon installation, or any
time thereafter, a user agent allows the user to inspect and, if
necessary, modify the [=start URL=] of an application.
</p>
<p>
A user agent MAY offer other protections against this form of
fingerprinting. For example, if a user clears data from an origin,
the user agent MAY offer to uninstall applications that are
[=manifest/within scope=] of that origin, thus removing the
potential fingerprint from the application's start URL.
</p>
</section>
</section>
<section>
<h3>
`id` member
</h3>
<p>
The [=manifest's=] <code><dfn data-export="" data-dfn-for=
"manifest">id</dfn></code> member is a <a>string</a> that represents
the <dfn>identity</dfn> for the application. The [=identity=] takes
the form of a URL, which is same origin as the [=start URL=].
</p>
<p>
The [=identity=] is used by user agents to uniquely identify the
application universally. When the user agent sees a manifest with an
[=identity=] that does not correspond to an already-installed
application, it SHOULD treat that manifest as a description of a
distinct application, even if it is served from the same URL as that
of another application. When the user agent sees a manifest where
|manifest|["id"] is [=url/equal=] (with [=URL/equals/exclude
fragments=] OPTIONALLY set to true) to the [=identity=] of an
already-installed application, it SHOULD be used as a signal that
this manifest is a replacement for the already-installed
application's manifest, and not a distinct application, even if it is
served from a different URL than the one seen previously.
</p>
<aside class="note" title="Excluding fragments is best practice">
Since the [=process the id member|processing algorithm=] removes the
[=URL/fragment=] from the <code>[=manifest/id=]</code> member, it is
not strictly necessary to [=URL/equals/exclude fragments=] when
checking for a matching application. However, since old versions of
this spec (and, possibly, old user agents) did not remove the
[=URL/fragment=] from the [=URL=] at parse time, and relied only on
[=URL/equals/exclude fragments|excluding fragments=] during
comparisons, historical app data could contain [=URL/fragments=] in
the <code>[=manifest/id=]</code>. Therefore, it is best practice for
user agents to [=URL/equals/exclude fragments=] even when comparing
two [=URLs=] that ought not to have fragments.
</aside>
<p class="note">
The [=identity=] can be used by a service that collects lists of web
applications to uniquely identify applications.
</p>
<p class="note">
The [=identity=] is processed like a URL but it doesn't point to a
resource that can be navigated to, so it's not required to be
[=URL/within scope=].
</p>
<p>
To <dfn>process the `id` member</dfn>, given [=ordered map=]
|json:JSON|, [=ordered map=] |manifest:ordered map|:
</p>
<ol class="algorithm">
<li>Set |manifest|["id"] to |manifest|["start_url"].
</li>
<li>If the type of |json|["id"] is not [=string=], return.
</li>
<li>If |json|["id"] is the empty string, return.
</li>
<li>Let |base origin| be |manifest|["start_url"]'s [=url/origin=].
</li>
<li>Let |id:URL| be the result of [=URL Parser|parsing=] |json|["id"]
with |base origin| as the base URL.
</li>
<li>If |id| is failure, return.
</li>
<li>If |id| is not [=same origin=] as |manifest|["start_url"],
return.
</li>
<li>Set |id|'s [=URL/fragment=] to null.
</li>
<li>Set |manifest|["id"] to |id|.
</li>
</ol>
<aside class="example" title="Resulting ids">
<p>
The table below shows some example `id`s resulting from the
[=process the `id` member=] steps.
</p>
<table class="data">
<tr>
<th>
|json|["id"]
</th>
<th>
|manifest|["start_url"]
</th>
<th>
|manifest|["id"]
</th>
</tr>
<tr>
<td>
<i>undefined</i>
</td>
<td>
"https://example.com/my-app/start"
</td>
<td>
"https://example.com/my-app/start"
</td>
</tr>
<tr>
<td>
<i>undefined</i>
</td>
<td>
"https://example.com/my-app/#here"
</td>
<td>
"https://example.com/my-app/"
</td>
</tr>
<tr>
<td>
""
</td>
<td>
"https://example.com/my-app/start"
</td>
<td>
"https://example.com/my-app/start"
</td>
</tr>
<tr>
<td>
"/"
</td>
<td>
"https://example.com/my-app/start"
</td>
<td>
"https://example.com/"
</td>
</tr>
<tr>
<td>
"foo"
</td>
<td>
"https://example.com/my-app/start"
</td>
<td>
"https://example.com/foo"
</td>
</tr>
<tr>
<td>
"foo?x=y"
</td>
<td>
"https://example.com/my-app/start"
</td>
<td>
"https://example.com/foo?x=y"
</td>
</tr>