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<!DOCTYPE html>
<html lang="en-US">
<head>
<meta charset="UTF-8">
<title>
Presentation API
</title>
<script src="https://www.w3.org/Tools/respec/respec-w3c-common" async
class="remove">
</script>
<script class="remove">
var respecConfig = {
specStatus: 'ED',
edDraftURI: 'https://w3c.github.io/presentation-api/',
shortName: 'presentation-api',
editors: [
{
w3cid: 68454,
name: 'Mark Foltz',
company: 'Google',
mailto: '[email protected]'
},
{
w3cid: 63802,
name: 'Dominik Röttsches',
company: 'Intel',
note: 'until April 2015'
}
],
previousMaturity: 'WD',
previousPublishDate: '2015-07-01',
otherLinks: [
{
key: 'Version history',
data: [
{
value: 'GitHub w3c/presentation-api/commits',
href: 'https://github.com/w3c/presentation-api/commits/'
}
]
},
{
key: 'Test suite',
data: [
{
value: 'GitHub web-platform-tests/presentation-api',
href: 'https://github.com/w3c/web-platform-tests/tree/master/presentation-api'
},
{
value: 'w3c-test.org/presentation-api/',
href: 'http://w3c-test.org/presentation-api/'
}
]
},
{
key: 'Participate',
data: [
{
value: 'GitHub w3c/presentation-api',
href: 'https://github.com/w3c/presentation-api/'
},
{
value: 'File an issue',
href: 'https://github.com/w3c/presentation-api/issues/new'
},
{
value: 'Open issues',
href: 'https://github.com/w3c/presentation-api/issues/'
},
{
value: 'Mailing-list ([email protected])',
href: 'https://lists.w3.org/Archives/Public/public-secondscreen/'
}
]
}
],
sotdAfterWGinfo: true,
wg: 'Second Screen Presentation Working Group',
wgURI: 'http://www.w3.org/2014/secondscreen/',
wgPublicList: 'public-secondscreen',
wgPatentURI: 'http://www.w3.org/2004/01/pp-impl/74168/status',
localBiblio: {
PROMGUIDE: {
title: 'Writing Promise-Using Specifications',
href: 'http://www.w3.org/2001/tag/doc/promises-guide',
authors: [
'Domenic Denicola'
],
status: 'finding',
publisher: 'W3C'
},
DIAL: {
title: 'DIscovery And Launch Protocol Specification',
href: 'http://www.dial-multiscreen.org/dial-protocol-specification',
authors: [
'Netflix',
'YouTube'
],
publisher: 'Netflix'
}
},
issueBase: "https://www.github.com/w3c/presentation-api/issues/"
// TODO: Uncomment when https://github.com/w3c/presentation-api/issues/228 is fixed
// githubAPI: "https://api.github.com/repos/w3c/presentation-api"
};
</script>
<style>
/* Note formatting taken from HTML5 spec */
.note { border-left-style: solid; border-left-width: 0.25em; background: none repeat scroll 0 0 #E9FBE9; border-color: #52E052; }
.note em, .warning em, .note i, .warning i { font-style: normal; }
p.note, div.note { padding: 0.5em 2em; }
span.note { padding: 0 2em; }
.note p:first-child { margin-top: 0; }
.note p:last-child { margin-bottom: 0; }
p.note:before { content: 'NOTE: '; }
.non-normative { border-left-style: solid; border-left-width: 0.25em; background: none repeat scroll 0 0 #E9FBE9; border-color: #52E052; }
p.non-normative:before { content: 'Non-normative: '; font-weight: bolder;}
p.non-normative, div.non-normative { padding: 0.5em 2em; }
.algorithm li {
margin-bottom: 0.5em;
}
.interface dd, .parameters dt {
margin-bottom: 0.5em;
}
code { color: orangered; }
table { border-collapse: collapse; border-style: hidden hidden none hidden; }
table thead, table tbody { border-bottom: solid; }
table td, table th { border-left: solid; border-right: solid; border-bottom: solid thin; vertical-align: top; padding: 0.2em; }
dfn { font-weight: bolder; font-style: normal; }
.copyright { font-size: small; }
.issue[id^='issue-'] > *:not([role='heading']) { display: none; }
</style>
</head>
<body>
<section id="abstract">
<p>
This specification defines an API to enable web content to access
external presentation-type displays and use them for presenting web
content.
</p>
</section>
<section id="sotd">
<p>
Since publication as Working Draft on <a href=
"https://www.w3.org/TR/2016/WD-presentation-api-20160211/">11 February
2016</a>, the Working Group has further refined some of the procedures,
notably those linked to the receiving user agent, specified the
algorithm for generating a presentation identifier, clarified the
expected behavior when a presentation is started using the default
presentation request, added recommendations for reusing the locale
settings of the controller in presentations, and further refined text
to ease testing. The Working Group also conducted horizontal reviews on
accessibility, internationalization, privacy, security and technical
architecture principles with the help of relevant groups at W3C.
</p>
<p>
The Working Group intends to publish a Candidate Recommendation once it
has fixed <a href=
"https://github.com/w3c/presentation-api/issues">remaining issues</a>
and made initial progress on the test suite. Wide reviews of this
document are encouraged.
</p>
</section>
<section class="informative">
<h2>
Introduction
</h2>
<p>
This specification aims to make <a>presentation displays</a> such as
projectors or connected TVs, available to the Web and takes into
account displays that are attached using wired (HDMI, DVI, or similar)
and wireless technologies (Miracast, Chromecast, DLNA, AirPlay, or
similar).
</p>
<p>
Devices with limited screen size lack the ability to show content to a
larger audience, for example, a group of colleagues in a conference
room, or friends and family at home. Showing content on an external
large <a>presentation display</a> helps to improve the perceived
quality and impact of the presented content.
</p>
<p>
At its core, this specification enables an exchange of messages between
a page that acts as the <a>controller</a> and another page that
represents the <a data-lt="receiving browsing context">presentation</a>
shown in the <a>presentation display</a>. How the messages are
transmitted is left to the UA in order to allow the use of
<a>presentation display</a> devices that can be attached in a wide
variety of ways. For example, when a <a>presentation display</a> device
is attached using HDMI or Miracast, the same UA that acts as the
<a>controller</a> renders the <a data-lt=
"receiving browsing context">presentation</a>. Instead of displaying
the <a data-lt="receiving browsing context">presentation</a> in another
window on the same device, however, it can use whatever means the
operating system provides for using the external <a>presentation
displays</a>. In such a case, both the <a>controller</a> and
<a data-lt="receiving browsing context">presentation</a> run on the
same UA and the operating system is used to route the <a>presentation
display</a> output to the <a>presentation display</a>. This is commonly
referred to as the <dfn><b id="1-ua">1-UA</b></dfn> case. This
specification imposes no requirements on the <a>presentation
display</a> devices connected in such a manner.
</p>
<p>
If the <a>presentation display</a> is able to render HTML documents and
communicate with the <a>controller</a>, the <a>controller</a> does not
need to render the <a data-lt=
"receiving browsing context">presentation</a>. In this case, the UA
acts as a proxy that requests the <a>presentation display</a> to show
and render the <a data-lt="receiving browsing context">presentation</a>
itself. This is commonly referred to as the <b id="2-ua">2-UA</b> case.
This way of attaching to displays could be enhanced in the future by
defining a standard protocol for delivering these types of messages
that display devices could choose to implement.
</p>
<p>
The API defined here is intended to be used with UAs that attach to
<a>presentation display</a> devices through any of the above means.
</p>
</section>
<section id="use-cases-and-requirements">
<h2>
Use cases and requirements
</h2>
<p>
Use cases and requirements are captured in a separate <a href=
"https://github.com/w3c/presentation-api/blob/gh-pages/uc-req.md">Presentation
API Use Cases and Requirements</a> document.
</p>
</section>
<section id="conformance">
<p>
Requirements phrased in the imperative as part of algorithms (such as
"strip any leading space characters" or "return false and terminate
these steps") are to be interpreted with the meaning of the key word
("MUST", "SHOULD", "MAY", etc.) used in introducing the algorithm.
</p>
<p>
Conformance requirements phrased as algorithms or specific steps may be
implemented in any manner, so long as the result is equivalent. (In
particular, the algorithms defined in this specification are intended
to be easy to follow, and not intended to be performant.)
</p>
<section>
<h3>
Conformance Classes
</h3>
<p>
This specification describes the conformance criteria for two classes
of <dfn data-lt="user agent">user agents</dfn>.
</p>
<dl>
<dt>
<dfn>Controlling user agent</dfn>
</dt>
<dd>
<p>
Web browsers that conform to the specifications of a
<a>controlling user agent</a> must be able to start and control
presentations by providing a <a>controlling browsing context</a>
as described in this specification. This context implements the
<a><code>Presentation</code></a>,
<a><code>PresentationConnection</code></a>,
<a><code>PresentationConnectionAvailableEvent</code></a>, and
<a><code>PresentationRequest</code></a> interfaces.
</p>
</dd>
<dt>
<dfn>Receiving user agent</dfn>
</dt>
<dd>
<p>
Web browsers that conform to the specifications of a <a>receiving
user agent</a> must be able to render presentations by providing
a <a>receiving browsing context</a> as described in this
specification. This context implements the
<a><code>Presentation</code></a>,
<a><code>PresentationConnection</code></a>,
<a><code>PresentationConnectionAvailableEvent</code></a>, and
<a><code>PresentationReceiver</code></a> interfaces.
</p>
</dd>
</dl>
<p>
One user agent may act both as a <a>controlling user agent</a> and as
a <a>receiving user agent</a>, if it provides both browsing contexts
and implements all of their required interfaces. This can happen when
the same user agent is able to host the <a>controlling browsing
context</a> and the <a>receiving browsing context</a> for a
presentation, as in the <a>1-UA</a> implementation of the API.
</p>
<p>
Conformance requirements phrased against a <a>user agent</a> apply
either to a <a>controlling user agent</a>, a <a>receiving user
agent</a> or to both classes, depending on the context.
</p>
</section>
</section>
<section>
<h2>
Terminology
</h2>
<p>
The terms <dfn><a href=
"http://www.w3.org/TR/html5/browsers.html#browsing-context">browsing
context</a></dfn>, <dfn><a href=
"https://www.w3.org/TR/html5/browsers.html#nested-browsing-contexts">nested
browsing context</a></dfn>, <dfn><a href=
"http://www.w3.org/TR/html5/webappapis.html#event-handlers">event
handler</a></dfn>, <dfn><a href=
"http://www.w3.org/TR/html5/webappapis.html#event-handler-event-type">event
handler event type</a></dfn>, <dfn data-lt="fire|fires"><a href=
"http://www.w3.org/TR/html5/infrastructure.html#concept-event-fire">firing
an event</a></dfn>, <dfn data-lt="fire a simple event"><a href=
"http://www.w3.org/TR/html5/webappapis.html#fire-a-simple-event">firing
a simple event</a></dfn>, <dfn><a href=
"http://www.w3.org/TR/html5/browsers.html#navigate">navigate</a></dfn>,
<dfn><a href=
"http://www.w3.org/TR/html5/webappapis.html#queue-a-task">queue a
task</a></dfn>, <dfn><a href=
"http://www.w3.org/TR/html5/infrastructure.html#concept-events-trusted">
trusted event</a></dfn>, <dfn><a href=
"http://www.w3.org/TR/html5/browsers.html#allowed-to-show-a-popup">allowed
to show a popup</a></dfn>, <dfn><a href=
"http://www.w3.org/TR/html5/browsers.html#top-level-browsing-context">top-level
browsing context</a></dfn>, <dfn><a href=
"https://www.w3.org/TR/html5/browsers.html#unload-a-document">unload a
document</a></dfn>, <dfn><a href=
"http://www.w3.org/TR/html5/browsers.html#session-history">session
history</a></dfn>, <dfn><a href=
"https://www.w3.org/TR/html5/browsers.html#sandboxing-flag-set">sandboxing
flag set</a></dfn>, <dfn><a href=
"https://www.w3.org/TR/html5/browsers.html#active-sandboxing-flag-set">active
sandboxing flag set</a></dfn>, <dfn><a href=
"https://www.w3.org/TR/html5/browsers.html#parse-a-sandboxing-directive">
parse a sandboxing directive</a></dfn>, <dfn><a href=
"http://www.w3.org/TR/html5/browsers.html#sandboxed-auxiliary-navigation-browsing-context-flag">
sandboxed auxiliary navigation browsing context flag</a></dfn>,
<dfn><a href=
"http://www.w3.org/TR/html5/browsers.html#sandboxed-top-level-navigation-browsing-context-flag">
sandboxed top-level navigation browsing context flag</a></dfn>, and
<dfn><a href=
"http://www.w3.org/TR/html5/webappapis.html#settings-object">settings
object</a></dfn> are defined in [[!HTML5]].
</p>
<p>
The term <dfn><a href=
"http://www.w3.org/TR/html51/infrastructure.html#in-parallel">in
parallel</a></dfn> is defined in [[!HTML51]].
</p>
<p>
This document provides interface definitions using the Web IDL standard
([[!WEBIDL]]). The terms <dfn><a href=
"https://heycam.github.io/webidl/#idl-promise">Promise</a></dfn>,
<dfn><a href=
"http://heycam.github.io/webidl/#idl-ArrayBuffer">ArrayBuffer</a></dfn>,
<dfn><a href=
"http://heycam.github.io/webidl/#idl-ArrayBufferView">ArrayBufferView</a></dfn>
are defined in [[!WEBIDL]].
</p>
<p>
The <dfn>term</dfn> throw in this specification is used as defined in
[[!WEBIDL]]. The following exception names are defined by WebIDL and
used by this specification:
</p>
<ul>
<li>
<dfn><code>NotAllowedError</code></dfn>
</li>
<li>
<dfn><code>InvalidAccessError</code></dfn>
</li>
<li>
<dfn><code>NotFoundError</code></dfn>
</li>
<li>
<dfn><code>NotSupportedError</code></dfn>
</li>
<li>
<dfn><code>OperationError</code></dfn>
</li>
<li>
<dfn><code>SecurityError</code></dfn>
</li>
<li>
<dfn><code>SyntaxError</code></dfn>
</li>
</ul>
<p>
The terms <dfn data-lt="resolve"><a href=
"http://www.w3.org/2001/tag/doc/promises-guide#resolve-promise">resolving
a Promise</a></dfn> and <dfn data-lt="reject"><a href=
"http://www.w3.org/2001/tag/doc/promises-guide#reject-promise">rejecting
a Promise</a></dfn> are used as explained in [[!PROMGUIDE]].
</p>
<p>
The term <dfn><a href="https://url.spec.whatwg.org/#url">URL</a></dfn>
is defined in the WHATWG URL standard [[!URL]].
</p>
<p>
The term <dfn><a href=
"http://dev.w3.org/2006/webapi/FileAPI/#blob">Blob</a></dfn> is defined
in the File API specification [[!FILEAPI]].
</p>
<p>
The header <dfn><a href=
"https://tools.ietf.org/html/rfc7231#section-5.3.5">Accept-Language</a></dfn>
is defined in HTTP 1/.1 [[!rfc7231]].
</p>
<p>
The term <dfn><a href=
"http://w3c.github.io/webrtc-pc/#idl-def-RTCDataChannel">RTCDataChannel</a></dfn>
is defined in the WebRTC API specification [[WEBRTC]].
</p>
<p>
The term <dfn><a href=
"http://tools.ietf.org/html/rfc6265#section-4.2">cookie store</a></dfn>
is defined in RFC 6265 [[COOKIES]].
</p>
<p>
The term <dfn><a href=
"https://tools.ietf.org/html/rfc4122">UUID</a></dfn> is defined in RFC
4122 [[rfc4122]].
</p>
<p>
The terms <dfn data-lt="permission|permissions"><a href=
"https://w3c.github.io/permissions/#idl-def-Permission">permission</a></dfn>
and <dfn><a href=
"https://w3c.github.io/permissions/#idl-def-PermissionState">permission
state</a></dfn> are defined in [[PERMISSIONS]].
</p>
<p>
The term <dfn data-lt="database|databases"><a href=
"http://www.w3.org/TR/IndexedDB/#database-concept">database</a></dfn>
is defined in [[INDEXEDDB]].
</p>
<p>
The terms <dfn><a href=
"http://www.w3.org/TR/webstorage/#the-localstorage-attribute"><code>localStorage</code></a></dfn>
and <dfn><a href=
"http://www.w3.org/TR/webstorage/#the-sessionstorage-attribute"><code>sessionStorage</code></a></dfn>
are defined in [[WEBSTORAGE]].
</p>
<p>
The terms <dfn><a href=
"https://www.w3.org/TR/mixed-content/#potentially-secure-origin">potentially
secure</a></dfn>, <dfn><a href=
"https://w3c.github.io/webappsec-mixed-content/#a-priori-authenticated-url">
a priori unauthenticated URL</a></dfn>, and <dfn><a href=
"https://w3c.github.io/webappsec-mixed-content/#categorize-settings-object">
prohibits mixed security contexts algorithm</a></dfn> are defined in
[[!MIXED-CONTENT]].
</p>
<p>
The term <dfn><a href="http://www.dial-multiscreen.org/">DIAL</a></dfn>
is defined in [[DIAL]].
</p>
</section>
<section>
<h2>
Examples
</h2>
<p>
This section shows example codes that highlight the usage of main
features of the Presentation API. In these examples,
<code>controller.html</code> implements the controller and
<code>presentation.html</code> implements the presentation. Both pages
are served from the domain <code>http://example.org</code>
(<code>http://example.org/controller.html</code> and
<code>http://example.org/presentation.html</code>). These examples
assume that the controlling page is managing one presentation at a
time. Please refer to the comments in the code examples for further
details.
</p>
<section>
<h3>
Monitor availability of presentation displays example
</h3>
<pre class="example highlight">
<!-- controller.html -->
<button id="presentBtn" style="display: none;">Present</button>
<script>
// The Present button is visible if at least one presentation display is available
var presentBtn = document.getElementById("presentBtn");
// It is also possible to use relative presentation URL e.g. "presentation.html"
var presUrl = "http://example.com/presentation.html";
// show or hide present button depending on display availability
var handleAvailabilityChange = function(available) {
presentBtn.style.display = available ? "inline" : "none";
};
// Promise is resolved as soon as the presentation display availability is
// known.
var request = new PresentationRequest(presUrl);
request.getAvailability().then(function(availability) {
// availability.value may be kept up-to-date by the controlling UA as long
// as the availability object is alive. It is advised for the web developers
// to discard the object as soon as it's not needed.
handleAvailabilityChange(availability.value);
availability.onchange = function() { handleAvailabilityChange(this.value); };
}).catch(function() {
// Availability monitoring is not supported by the platform, so discovery of
// presentation displays will happen only after request.start() is called.
// Pretend the devices are available for simplicity; or, one could implement
// a third state for the button.
handleAvailabilityChange(true);
});
</script>
</pre>
</section>
<section>
<h3>
Starting a new presentation example
</h3>
<pre class="example highlight">
<!-- controller.html -->
<script>
presentBtn.onclick = function () {
// Start new presentation.
request.start()
// The connection to the presentation will be passed to setConnection on
// success.
.then(setConnection);
// Otherwise, the user canceled the selection dialog or no screens were
// found.
};
</script>
</pre>
</section>
<section>
<h3>
Reconnect to a presentation example
</h3>
<pre class="example highlight">
<!-- controller.html -->
<button id="reconnectBtn" style="display: none;">Reconnect</button>
<script>
var reconnect = function () {
// read presId from localStorage if exists
var presId = localStorage["presId"];
// presId is mandatory when reconnecting to a presentation.
if (!!presId) {
request.reconnect(presId)
// The new connection to the presentation will be passed to
// setConnection on success.
.then(setConnection);
// No connection found for presUrl and presId, or an error occurred.
}
};
// On navigation of the controller, reconnect automatically.
document.addEventListener("DOMContentLoaded", reconnect);
// Or allow manual reconnection.
reconnectBtn.onclick = reconnect;
</script>
</pre>
</section>
<section>
<h3>
Presentation initation by the controlling UA example
</h3>
<pre class="example highlight">
<!-- controller.html -->
<!-- Setting presentation.defaultRequest allows the page to specify the
PresentationRequest to use when the controlling UA initiates a
presentation. -->
<script>
navigator.presentation.defaultRequest = new PresentationRequest(defaultUrl);
navigator.presentation.defaultRequest.onconnectionavailable = function(evt) {
setConnection(evt.connection);
};
</script>
</pre>
</section>
<section>
<h3>
Monitor connection's state and exchange data example
</h3>
<pre class="example highlight">
<!-- controller.html -->
<button id="disconnectBtn" style="display: none;">Disconnect</button>
<button id="terminateBtn" style="display: none;">Stop</button>
<script>
var connection;
// The Disconnect and Stop buttons are visible if there is a connected presentation
var disconnectBtn = document.getElementById("disconnectBtn");
var stopBtn = document.getElementById("stopBtn");
stopBtn.onclick = function () { connection && connection.terminate(); };
var setConnection = function (theConnection) {
// Disconnect from existing presentation, if any
close();
// Set the new connection and save the presentation ID
connection = theConnection;
localStorage["presId"] = connection.id;
// monitor connection's state
connection.onconnect = function () {
// Allow the user to disconnect from or terminate the presentation
disconnectBtn.style.display = "inline";
stopBtn.style.display = "inline";
reconnectBtn.style.display = "none";
// register message handler
this.onmessage = function (message) {
console.log("receive message", message.data);
};
// send initial message to presentation page
this.send("say hello");
};
connection.onclose = reset;
connection.onterminate = function () {
// remove presId from localStorage if exists
delete localStorage["presId"];
// Reset the UI
reset();
};
};
var reset = function () {
connection = null;
disconnectBtn.style.display = "none";
stopBtn.style.display = "none";
reconnectBtn.style.display = localStorage["presId"] ? "inline" : "none";
};
var close = function () { connection && connection.close(); };
disconnectBtn.onclick = close;
</script>
</pre>
</section>
<section>
<h3>
Monitor available connection(s) and say hello
</h3>
<pre class="example highlight">
<!-- receiver.html -->
<script>
var addConnection = function(connection) {
connection.onconnect = function () {
this.onmessage = function (message) {
if (message.data == "say hello")
this.send("hello");
};
};
};
navigator.presentation.receiver.connectionList.then(function (list) {
list.connections.map(function (connection) {
addConnection(connection);
});
list.connections.onconnectionavailable = function (connections) {
addConnection(connections[connections.length - 1]);
};
});
</script>
</pre>
</section>
<section>
<h3>
Passing locale information with a message
</h3>
<pre class="example highlight">
<!-- controller.html -->
<script>
connection.send("{string: '你好，世界!', lang: 'zh-CN'}");
connection.send("{string: 'こんにちは、世界!', lang: 'ja'}");
connection.send("{string: '안녕하세요, 세계!', lang: 'ko'}");
connection.send("{string: 'Hello, world!', lang: 'en-US'}");
</script>
<!-- receiver.html -->
<script>
connection.onmessage = function (message) {
var messageObj = JSON.parse(message);
var spanElt = document.createElement("SPAN");
spanElt.lang = messageObj.lang;
spanElt.textContent = messageObj.string;
document.appendChild(spanElt);
};
</script>
</pre>
</section>
</section>
<section>
<h2>
API
</h2>
<section>
<h3>
Common idioms
</h3>
<p>
A <dfn lt="presentation display|presentation displays">presentation
display</dfn> refers to an external screen available to the user
agent via an implementation specific connection technology.
</p>
<p>
A <dfn lt=
"presentation connection|presentation connections">presentation
connection</dfn> is an object relating a <a>controlling browsing
context</a> to its <a>receiving browsing context</a> and enables
two-way-messaging between them. Each <a>presentation connection</a>
has a <dfn>presentation connection state</dfn>, a unique <dfn lt=
"presentation identifier|presentation identifiers">presentation
identifier</dfn> to distinguish it from other <a>presentations</a>,
and a <dfn>presentation URL</dfn> that is a <a>URL</a> used to create
or reconnect to the <a>presentation</a>. A <dfn>valid presentation
identifier</dfn> consists of alphanumeric ASCII characters only and
is at least 16 characters long.
</p>
<p>
A <dfn lt=
"controlling browsing context|controlling browsing contexts">controlling
browsing context</dfn> (or <dfn>controller</dfn> for short) is a
<a>browsing context</a> that has connected to a <a>presentation</a>
by calling <code><a for="PresentationRequest">start</a>()</code> or
<code><a for="PresentationRequest">reconnect</a>()</code>, or
received a <a>presentation connection</a> via a <a for=
"PresentationRequest">connectionavailable</a> event.
</p>
<p>
The <dfn data-lt=
"receiving browsing context|receiving browsing contexts">receiving
browsing context</dfn> (or <dfn for="idiom" data-lt=
"presentations">presentation</dfn> for short) is the browsing context
responsible for rendering to a <a>presentation display</a>. A
<a>receiving browsing context</a> can reside in the same user agent
as the <a>controlling browsing context</a> or a different one. A
<a>receiving browsing context</a> is created by following the steps
to <a>create a receiving browsing context</a>.
</p>
<p>
In a procedure, the <dfn>destination browsing context</dfn> is the
<a>receiving browsing context</a> when the procedure is initiated at
the <a>controlling browsing context</a>, or the <a>controlling
browsing context</a> if it is initiated at the <a>receiving browsing
context</a>.
</p>
<p>
The <dfn>set of controlled presentations</dfn>, initially empty,
contains the <a>presentation connections</a> created by the
<a>controlling browsing contexts</a> for the <a>controlling user
agent</a> (or a specific user profile within that user agent). The
<a>set of controlled presentations</a> is represented by a list of
<a>PresentationConnection</a> objects that represent the underlying
<a>presentation connections</a>. Several
<a>PresentationConnection</a> objects may share the same
<a>presentation URL</a> and <a>presentation identifier</a> in that
set, but there can be only one <a>PresentationConnection</a> with a
specific <a>presentation URL</a> and <a>presentation identifier</a>
for a given <a>controlling browsing context</a>.
</p>
<p>
The <dfn>set of presentation controllers</dfn>, initially empty,
contains the <a>presentation connections</a> created by a
<a>receiving browsing context</a> for the <a>receiving user
agent</a>. The <a>set of presentation controllers</a> is represented
by a list of <a>PresentationConnection</a> objects that represent the
underlying <a>presentation connections</a>. All <a>presentation
connections</a> in this set share the same <a>presentation URL</a>
and <a>presentation identifier</a>.
</p>
<p>
In a <a>receiving browsing context</a>, the <dfn>presentation
controllers monitor</dfn>, initially set to <code>null</code>,
exposes the current <a>set of presentation controllers</a> to the
receiving application. The <a>presentation controllers monitor</a> is
represented by a <a>PresentationConnectionList</a>.
</p>
<p>
In a <a>receiving browsing context</a>, the <dfn>presentation
controllers promise</dfn>, which is initially set to
<code>null</code>, provides the <a>presentation controllers
monitor</a> once the initial <a>presentation connection</a> is
established. The <a>presentation controllers promise</a> is
represented by a <a>Promise</a> that resolves with the
<a>presentation controllers monitor</a>.
</p>
</section>
<section>
<h3>
Interface <code>Presentation</code>
</h3>
<pre class="idl">
partial interface Navigator {
[SameObject] readonly attribute Presentation? presentation;
};
interface Presentation {
};
</pre>
<p>
The <dfn for="Navigator"><code>presentation</code></dfn> attribute is
used to retrieve an instance of the <a><code>Presentation</code></a>
interface. It MUST return the <a><code>Presentation</code></a>
instance.
</p>
<section>
<h4>
Controlling user agent
</h4>
<pre class="idl idl-controlling-ua">
partial interface Presentation {
attribute PresentationRequest? defaultRequest;
};
</pre>
<p>
In a <a>controlling user agent</a>, the <dfn for=
"Presentation"><code>defaultRequest</code></dfn> attribute MUST
return the <a>default presentation request</a> if any,
<code>null</code> otherwise. In a <a>receiving browsing
context</a>, it MUST return <code>null</code>.
</p>
<p>
If set by the <a>controller</a>, the value of the <a for=
"Presentation">defaultRequest</a> attribute SHOULD be used by the
<a>controlling user agent</a> as the <dfn>default presentation
request</dfn> for that <a>controlling browsing context</a>. When
the <a>controlling user agent</a> wishes to initiate a
<a>PresentationConnection</a> on the behalf of that browsing
context, it MUST <a>start a presentation</a> using the <a>default
presentation request</a> for the <a>controller</a> (as if the
controller had called <code>defaultRequest.start()</code>).
</p>
<p>
The <a>controlling user agent</a> SHOULD initiate presentation
using the <a>default presentation request</a> only when the user
has expressed an intention to do so via a user gesture, for example
by clicking a button in the browser.
</p>
<div class="note">
If a <a>controlling user agent</a> does not support initiation of a
<a>presentation connection</a> from the browser chrome, setting
<code>defaultRequest</code> will have no effect.
</div>
<div class="note">
Some <a data-lt="controlling user agent">controlling user
agents</a> may allow the user to initiate a default <a>presentation
connection</a> and select a <a>presentation display</a> with the
same user gesture. For example, the browser chrome could allow the
user to pick a display from a menu, or allow the user to tap on an
<a href="https://nfc-forum.org/">Near Field Communications
(NFC)</a> enabled display. In this case, when the <a>controlling
user agent</a> asks for permission while <a data-lt=
"start a presentation">starting a presentation</a>, the browser
could offer that display as the default choice, or consider the
gesture as granting permission for the display and bypass display
selection entirely.
</div>
</section>
<section>
<h4>
Receiving user agent
</h4>
<pre class="idl idl-receiving-ua">
partial interface Presentation {
[SameObject] readonly attribute PresentationReceiver? receiver;
};
</pre>
<p>
In a <a>receiving user agent</a>, the <dfn for=
"Presentation"><code>receiver</code></dfn> attribute MUST return
the <a><code>PresentationReceiver</code></a> instance associated
with the <a>receiving browsing context</a> and created by the
<a>receiving user agent</a> when the <a>receiving browsing
context</a> is created. In any other <a>browsing context</a>, it
MUST return <code>null</code>.
</p>
<p>
A user agent that is a <a>receiving user agent</a> but not a
<a>controlling user agent</a> MUST always return <code>null</code>
for the <a for="Presentation">defaultRequest</a> attribute. It MUST
treat setting the <a for="Presentation">defaultRequest</a>
attribute as a no-op.
</p>
<p>
A user agent that is a <a>controlling user agent</a> but not a
<a>receiving user agent</a> MUST always return <code>null</code>
for the <a for="Presentation">receiver</a> attribute.
</p>
</section>
</section>
<section>
<h3>
Interface <a><code>PresentationRequest</code></a>
</h3>
<pre class="idl">
[Constructor(DOMString url)]
interface PresentationRequest : EventTarget {
Promise<PresentationConnection> start();
Promise<PresentationConnection> reconnect(DOMString presentationId);
Promise<PresentationAvailability> getAvailability();
attribute EventHandler onconnectionavailable;
};
</pre>
<p>
A <a><code>PresentationRequest</code></a> object is associated with a
request to initiate or reconnect to a presentation made by a
<a>controlling browsing context</a>. The
<a><code>PresentationRequest</code></a> object MUST be implemented in
a <a>controlling browsing context</a> provided by a <a>controlling
user agent</a>.
</p>
<p>
When a <a><code>PresentationRequest</code></a> is constructed, the
given <code>url</code> MUST be used as the <dfn>presentation request
URL</dfn> which is the <a>presentation URL</a> for the
<a><code>PresentationRequest</code></a> instance.
</p>
<section>
<h4>
Constructing a <code>PresentationRequest</code>
</h4>
<p>
When the <code>PresentationRequest</code> constructor is called,
the <a>controlling user agent</a> MUST run these steps:
</p>
<dl>
<dt>
Input
</dt>
<dd>
<var>url</var>, the <a>presentation request URL</a>
</dd>
<dt>
Output
</dt>
<dd>
A <code>PresentationRequest</code> object
</dd>
</dl>
<ol>
<li>Resolve <var>url</var> relative to the API base URL specified
by the entry <a>settings object</a>, and let
<var>presentationUrl</var> be the resulting absolute URL, if any.
</li>
<li>If the resolve a URL algorithm failed, then throw a
<a>SyntaxError</a> exception and abort the remaining steps.
</li>
<li>Construct a new <code>PresentationRequest</code> object with
<var>presentationUrl</var> as the constructor argument and return
it.
</li>
</ol>
</section>
<section>
<h4>
Starting a presentation
</h4>
<p>
When the <code><dfn for="PresentationRequest">start</dfn></code>
method is called, the <a>user agent</a> MUST run the following
steps to <dfn>start a presentation</dfn>:
</p>
<dl>
<dt>
Input
</dt>
<dd>
<var>presentationRequest</var>, the
<code>PresentationRequest</code> object
</dd>
<dd>
<var>presentationUrl</var>, the <a>presentation request URL</a>
</dd>
<dt>
Output
</dt>
<dd>
A <a>Promise</a>
</dd>
</dl>
<ol>
<li>If the algorithm isn't <a>allowed to show a popup</a>, return a
<a>Promise</a> rejected with an <a>InvalidAccessError</a> exception
and abort these steps.
</li>
<li>Using the document's <a>settings object</a>, run the
<a>prohibits mixed security contexts algorithm</a>.
</li>
<li>If the result of the algorithm is <code>"Prohibits Mixed
Security Contexts"</code> and <var>presentationUrl</var> is an <a>
a priori unauthenticated URL</a>, then return a <a>Promise</a>
rejected with a <a>SecurityError</a> and abort these steps.
</li>
<li>If the document object's <a>active sandboxing flag set</a> has
the <a>sandboxed presentation browsing context flag</a> set, then
return a <a>Promise</a> rejected with a <a>SecurityError</a> and
abort these steps.
</li>