fullscreen.bs

<pre class=metadata>
Group: WHATWG
H1: Fullscreen API
Shortname: fullscreen
Text Macro: TWITTER fullscreenapi
Text Macro: LATESTRD 2024-07
Abstract: The Fullscreen API standard defines an API for elements to display themselves fullscreen.
Translation: ja https://triple-underscore.github.io/fullscreen-ja.html
Translation: zh-Hans https://htmlspecs.com/fullscreen/
Markup Shorthands: css no
</pre>

<pre class=link-defaults>
spec:dom
    type:dfn; for:/; text:document
    type:dfn; for:/; text:element
    type:interface; text:Document
spec:infra
    type:dfn; for:set; text:for each
    type:dfn; text:string
spec:css-position-4
    type:selector; text: ::backdrop
    type:dfn; text:top layer
</pre>

<pre class=anchors>
urlPrefix: https://w3c.github.io/screen-orientation/#dfn-
    type: dfn
        text: triggered by a user generated orientation change
</pre>

<pre class=biblio>
{
    "CSS": {
        "aliasOf": "CSS2"
    },
    "SVG": {
        "aliasOf": "SVG11"
    }
}
</pre>



<h2 id=terminology>Terminology</h2>

<p>This specification depends on the Infra Standard. [[!INFRA]]

<p>Most terminology used in this specification is from CSS, DOM, HTML, and Web IDL. [[!CSS]]
[[!DOM]] [[!HTML]] [[!WEBIDL]]



<h2 id=model>Model</h2>

<p>All <a>elements</a> have an associated <dfn>fullscreen flag</dfn>. Unless stated otherwise it is
unset.

<p>All <{iframe}> <a>elements</a> have an associated <dfn>iframe fullscreen flag</dfn>. Unless
stated otherwise it is unset.

<p>All <a for=/>documents</a> have an associated <dfn export>fullscreen element</dfn>. The
<a>fullscreen element</a> is the topmost <a>element</a> in the <a for=/>document</a>'s
<a>top layer</a> whose <a>fullscreen flag</a> is set, if any, and null otherwise.

<p>All <a for=/>documents</a> have an associated <dfn>list of pending fullscreen events</dfn>, which
is an <a>ordered set</a> of (<a>string</a>, <a>element</a>) <a>tuples</a>. It is initially empty.

<p>To <dfn>fullscreen an <var>element</var></dfn>:

<ol>
 <li><p>Let <var>hideUntil</var> be the result of running <a>topmost popover ancestor</a> given
 <var>element</var>, null, and false.

 <li><p>If <var>hideUntil</var> is null, then set <var>hideUntil</var> to <var>element</var>'s
 <span>node document</span>.

 <li><p>Run <a>hide all popovers until</a> given <var>hideUntil</var>, false, and true.

 <li><p>Set <var>element</var>'s <a>fullscreen flag</a>.

 <li><p><a>Remove from the top layer immediately</a> given <var>element</var>.

 <li><a>Add to the top layer</a> given <var>element</var>.
</ol>

<p>To <dfn>unfullscreen an <var>element</var></dfn>, unset <var>element</var>'s
<a>fullscreen flag</a> and <a>iframe fullscreen flag</a> (if any), and
<a>remove from the top layer immediately</a> given <var>element</var>.

<p>To <dfn>unfullscreen a <var>document</var></dfn>,
<a lt="unfullscreen an element">unfullscreen</a> all <a>elements</a>, within <var>document</var>'s
<a>top layer</a>, whose <a>fullscreen flag</a> is set.

<hr>

<div algorithm>
<p>To <dfn>fully exit fullscreen</dfn> a <a for=/>document</a> <var>document</var>, run these steps:

<ol>
 <li><p>If <var>document</var>'s <a>fullscreen element</a> is null, terminate these steps.

 <li><p><a lt="unfullscreen an element">Unfullscreen elements</a> whose <a>fullscreen flag</a> is
 set, within <var>document</var>'s <a>top layer</a>, except for <var>document</var>'s
 <a>fullscreen element</a>.

 <li><p><a>Exit fullscreen</a> <var>document</var>.
</ol>
</div>

<div algorithm="fullscreen removing steps">
<p id=removing-steps>Whenever the <a>removing steps</a> run with a <var>removedNode</var>, run
these steps:

<ol>
 <li><p>Let <var>document</var> be <var>removedNode</var>'s <a>node document</a>.

 <li><p>Let <var>nodes</var> be <var>removedNode</var>'s
 <a>shadow-including inclusive descendants</a> that have their <a>fullscreen flag</a> set, in
 <a>shadow-including tree order</a>.

 <li>
  <p><a>For each</a> <var>node</var> in <var>nodes</var>:

  <ol>
   <li><p>If <var>node</var> is <var>document</var>'s <a>fullscreen element</a>,
   <a>exit fullscreen</a> <var>document</var>.

   <li><p>Otherwise, <a lt="unfullscreen an element">unfullscreen <var>node</var></a>.

   <li>
    <p>If <var>document</var>'s <a>top layer</a> <a for=set>contains</a> <var>node</var>,
    <a>remove from the top layer immediately</a> given <var>node</var>.

    <p class=note>Other specifications can add and remove elements from <a>top layer</a>, so
    <var>node</var> might not be <var>document</var>'s <a>fullscreen element</a>. For example,
    <var>node</var> could be an open <{dialog}> element.
  </ol>
</ol>
</div>

<p>Whenever the <a>unloading document cleanup steps</a> run with a <var>document</var>,
<a>fully exit fullscreen</a> <var>document</var>.

<hr>

<p><dfn>Fullscreen is supported</dfn> if there is no previously-established user preference,
security risk, or platform limitation.

<hr>

<div algorithm>
<p>To <dfn>run the fullscreen steps</dfn> for a <a>document</a> <var>document</var>, run these
steps:

<ol>
 <li><p>Let <var>pendingEvents</var> be <var>document</var>'s
 <a>list of pending fullscreen events</a>.

 <li><p><a for=set>Empty</a> <var>document</var>'s <a>list of pending fullscreen events</a>.

 <li>
  <p><a>For each</a> (<var>type</var>, <var>element</var>) in <var>pendingEvents</var>:

  <ol>
   <li><p>Let <var>target</var> be <var>element</var> if <var>element</var> is <a>connected</a>
   and its <a>node document</a> is <var>document</var>, and otherwise let <var>target</var> be
   <var>document</var>.

   <li><p><a>Fire an event</a> named <var>type</var>, with its {{Event/bubbles}} and
   {{Event/composed}} attributes set to true, at <var>target</var>.
  </ol>
</ol>

<p class=note>These steps integrate with the <a for=/>event loop</a> defined in HTML. [[!HTML]]
</div>



<h2 id=api>API</h2>

<pre class=idl>
enum FullscreenNavigationUI {
  "auto",
  "show",
  "hide"
};

dictionary FullscreenOptions {
  FullscreenNavigationUI navigationUI = "auto";
};

partial interface Element {
  Promise&lt;undefined> requestFullscreen(optional FullscreenOptions options = {});

  attribute EventHandler onfullscreenchange;
  attribute EventHandler onfullscreenerror;
};

partial interface Document {
  [LegacyLenientSetter] readonly attribute boolean fullscreenEnabled;
  [LegacyLenientSetter, Unscopable] readonly attribute boolean fullscreen; // historical

  Promise&lt;undefined> exitFullscreen();

  attribute EventHandler onfullscreenchange;
  attribute EventHandler onfullscreenerror;
};

partial interface mixin DocumentOrShadowRoot {
  [LegacyLenientSetter] readonly attribute Element? fullscreenElement;
};
</pre>
<!-- The event handler attributes are intentially not in a partial DocumentAndElementEventHandlers
     interface, which is implemented by Document and HTMLElement, not Element. -->

<dl class=domintro>
 <dt><code><var>promise</var> = <var>element</var> . <a method for=Element lt=requestFullscreen()>requestFullscreen([<var>options</var>])</a></code>
 <dd>
  Displays <var>element</var> fullscreen and resolves <var>promise</var> when done.

  When supplied, <var>options</var>'s {{FullscreenOptions/navigationUI}} member indicates whether
  showing navigation UI while in fullscreen is preferred or not. If set to
  "{{FullscreenNavigationUI/show}}", navigation simplicity is preferred over screen space, and if
  set to "{{FullscreenNavigationUI/hide}}", more screen space is preferred. User agents are always
  free to honor user preference over the application's. The default value
  "{{FullscreenNavigationUI/auto}}" indicates no application preference.

 <dt><code><var>document</var> . {{Document/fullscreenEnabled}}</code>
 <dd><p>Returns true if <var>document</var> has the ability to display <a>elements</a> fullscreen
 and <a>fullscreen is supported</a>, or false otherwise.

 <dt><code><var>promise</var> = <var>document</var> . {{Document/exitFullscreen()}}</code>
 <dd><p>Stops <var>document</var>'s <a>fullscreen element</a> from being displayed fullscreen and
 resolves <var>promise</var> when done.

 <dt><code><var>document</var> . {{DocumentOrShadowRoot/fullscreenElement}}</code>
 <dd><p>Returns <var>document</var>'s <a>fullscreen element</a>.

 <dt><code><var>shadowroot</var> . {{DocumentOrShadowRoot/fullscreenElement}}</code>
 <dd><p>Returns <var>shadowroot</var>'s <a>fullscreen element</a>.
</dl>

<p>A <dfn>fullscreen element ready check</dfn> for an <a>element</a> <var>element</var> returns true
if all of the following are true, and false otherwise:

<ul>
 <li><p><var>element</var> is <a>connected</a>.

 <li><p><var>element</var>'s <a>node document</a> is <a>allowed to use</a> the "<code><a
 data-lt="fullscreen-feature">fullscreen</a></code>" feature.
 <!-- cross-process, recursive -->

 <li><p><var>element</var> <a for=Element>namespace</a> is not the <a>HTML namespace</a> or
 <var>element</var>'s <a>popover visibility state</a> is <a for="popover visibility
 state">hidden</a>.
</ul>

<div algorithm="requestFullscreen(options)">
<p>The <dfn method for=Element><code>requestFullscreen(<var>options</var>)</code></dfn> method steps
are:

<ol>
 <li><p>Let <var>pendingDoc</var> be <a>this</a>'s <a>node document</a>.

 <li><p>Let <var>promise</var> be a new promise.

 <li><p>If <var>pendingDoc</var> is not <a>fully active</a>, then reject <var>promise</var> with a
 {{TypeError}} exception and return <var>promise</var>.

 <li><p>Let <var>error</var> be false.

 <li>
  <p>If any of the following conditions are false, then set <var>error</var> to true:

  <ul>
   <li><p><a>This</a>'s <a for=Element>namespace</a> is the <a>HTML namespace</a> or
   <a>this</a> is an
   <a href=https://www.w3.org/TR/SVG11/struct.html#SVGElement>SVG <code>svg</code></a> or
   <a href=https://www.w3.org/Math/draft-spec/chapter2.html#interf.toplevel>MathML <code>math</code></a>
   element. [[!SVG]] [[!MATHML]]

   <li><p><a>This</a> is not a <{dialog}> element.

   <li><p>The <a>fullscreen element ready check</a> for <a>this</a> returns true.

   <li><p><a>Fullscreen is supported</a>.

   <li><p><a>This</a>'s <a>relevant global object</a> has <a>transient activation</a> or the
   algorithm is <a>triggered by a user generated orientation change</a>.
  </ul>

 <li><p>If <var>error</var> is false, then <a>consume user activation</a> given
 <var>pendingDoc</var>'s <a>relevant global object</a>.

 <li><p>Return <var>promise</var>, and run the remaining steps <a>in parallel</a>.

 <li>
  <p>If <var>error</var> is false, then resize <var>pendingDoc</var>'s <a>node navigable</a>'s
  <a for=navigable>top-level traversable</a>'s <a for=navigable>active document</a>'s viewport's
  dimensions, optionally taking into account
  <var>options</var>["{{FullscreenOptions/navigationUI}}"]:
  <!-- cross-process -->

  <table>
    <thead>
      <tr>
      <th>value</th>
      <th>viewport dimensions</th>
      </tr>
    </thead>
    <tbody>
      <tr>
        <td>"<dfn enum-value for="FullscreenNavigationUI"><code>hide</code></dfn>"</td>
        <td>full dimensions of the screen of the output device</td>
      </tr>
      <tr>
        <td>"<dfn enum-value for="FullscreenNavigationUI"><code>show</code></dfn>"</td>
        <td>dimensions of the screen of the output device clamped to allow the user agent to show page navigation controls</td>
      </tr>
      <tr>
        <td>"<dfn enum-value for="FullscreenNavigationUI"><code>auto</code></dfn>"</td>
        <td>user-agent defined, but matching one of the above</td>
      </tr>
    </tbody>
  </table>

  <p>Optionally display a message how the end user can revert this.

 <li>
  <p>If any of the following conditions are false, then set <var>error</var> to true:

  <ul>
   <li><p><a>This</a>'s <a>node document</a> is <var>pendingDoc</var>.

   <li><p>The <a>fullscreen element ready check</a> for <a>this</a> returns true.
   <!-- cross-process; check is only needed on pending as it is recursive already -->
  </ul>

 <li>
  <p>If <var>error</var> is true:

  <ol>
   <li><p><a for=set>Append</a> ({{fullscreenerror}}, <a>this</a>) to
   <var>pendingDoc</var>'s <a>list of pending fullscreen events</a>.

   <li><p>Reject <var>promise</var> with a {{TypeError}} exception and terminate these
   steps.
  </ol>

 <li><p>Let <var>fullscreenElements</var> be an <a>ordered set</a> initially consisting of
 <a>this</a>.

 <li>
  <p>While true:

  <ol>
   <li><p>Let <var>last</var> be the last <a for=list>item</a> of <var>fullscreenElements</var>.

   <li><p>Let <var>container</var> be <var>last</var>'s <a>node navigable</a>'s
   <a for=navigable>container</a>.

   <li><p>If <var>container</var> is null, then <a>break</a>.

   <li><p><a for=set>Append</a> <var>container</var> to <var>fullscreenElements</var>.
  </ol>
 </li>
 <!-- cross-process -->

 <li>
  <p><a>For each</a> <var>element</var> in <var>fullscreenElements</var>:

  <ol>
   <li><p>Let <var>doc</var> be <var>element</var>'s <a>node document</a>.

   <li>
    <p>If <var>element</var> is <var>doc</var>'s <a>fullscreen element</a>, <a>continue</a>.

    <p class=note>No need to notify observers when nothing has changed.

   <li><p>If <var>element</var> is <a>this</a> and <a>this</a> is an <{iframe}>
   <a>element</a>, then set <var>element</var>'s <a>iframe fullscreen flag</a>.

   <li><p><a lt="fullscreen an element">Fullscreen <var>element</var></a> within <var>doc</var>.

   <li><p><a for=set>Append</a> ({{fullscreenchange}}, <var>element</var>) to
   <var>doc</var>'s <a>list of pending fullscreen events</a>.
  </ol>

  <p class=note>The order in which elements are <a lt="fullscreen an element">fullscreened</a>
  is not observable, because <a>run the fullscreen steps</a> is invoked in <a>tree order</a>.

 <li><p>Resolve <var>promise</var> with undefined.
</ol>

<p class=note>Implementations with out-of-process <a for=/>navigables</a> are left as an exercise
to the reader. Input welcome on potential improvements.
</div>

<p>The <dfn attribute for=Document><code>fullscreenEnabled</code></dfn> getter steps are to return
true if <a>this</a> is <a>allowed to use</a> the "<code><a
data-lt="fullscreen-feature">fullscreen</a></code>" feature and <a>fullscreen is supported</a>, and
false otherwise.

<p>The <dfn attribute for=Document><code>fullscreen</code></dfn> getter steps are to return false if
<a>this</a>'s <a>fullscreen element</a> is null, and true otherwise.

<p class=note>Use the {{DocumentOrShadowRoot/fullscreenElement}} attribute instead.

<div algorithm>
<p>The
<dfn attribute for=DocumentOrShadowRoot id=dom-document-fullscreenelement><code>fullscreenElement</code></dfn>
getter steps are:

<ol>
 <li><p>If <a>this</a> is a <a for=/>shadow root</a> and its <a for=DocumentFragment>host</a> is not
 <a>connected</a>, then return null.

 <li><p>Let <var>candidate</var> be the result of <a>retargeting</a> <a>fullscreen element</a>
 against <a>this</a>.

 <li><p>If <var>candidate</var> and <a>this</a> are in the same <a>tree</a>, then return
 <var>candidate</var>.

 <li><p>Return null.
</ol>
</div>

<p>A <a>document</a> is said to be a <dfn>simple fullscreen document</dfn> if there is exactly one
<a>element</a> in its <a>top layer</a> that has its <a>fullscreen flag</a> set.

<p class=note>A <a>document</a> with two <a>elements</a> in its <a>top layer</a> can be a
<a>simple fullscreen document</a>. For example, in addition to the <a>fullscreen element</a> there
could be an open <{dialog}> element.

<div algorithm>
<p>To <dfn>collect documents to unfullscreen</dfn> given <var>doc</var>, run these steps:

<ol>
 <li><p>Let <var>docs</var> be an <a>ordered set</a> consisting of <var>doc</var>.

 <li>
  <p><a>While</a> true:

  <ol>
   <li><p>Let <var>lastDoc</var> be <var>docs</var>'s last <a for=/>document</a>.

   <li><p>Assert: <var>lastDoc</var>'s <a>fullscreen element</a> is not null.

   <li><p>If <var>lastDoc</var> is not a <a>simple fullscreen document</a>, <a>break</a>.

   <li><p>Let <var>container</var> be <var>lastDoc</var>'s <a>node navigable</a>'s
   <a for=navigable>container</a>.

   <li><p>If <var>container</var> is null, then <a>break</a>.

   <li><p>If <var>container</var>'s <a>iframe fullscreen flag</a> is set, <a>break</a>.

   <li><p><a for=set>Append</a> <var>container</var>'s <a>node document</a> to <var>docs</var>.
  </ol>

 <li><p>Return <var>docs</var>.

 <p class=note>This is the set of documents for which the <a>fullscreen element</a> will be
 <a lt="unfullscreen an element">unfullscreened</a>, but the last document in <var>docs</var> might
 have more than one <a>element</a> in its <a>top layer</a> with the <a>fullscreen flag</a> set,
 in which case that document will still remain in fullscreen.
</ol>
</div>

<div algorithm>
<p>To <dfn>exit fullscreen</dfn> a <a for=/>document</a> <var>doc</var>, run these steps:

<ol>
 <li><p>Let <var>promise</var> be a new promise.

 <li><p>If <var>doc</var> is not <a>fully active</a> or <var>doc</var>'s <a>fullscreen element</a>
 is null, then reject <var>promise</var> with a {{TypeError}} exception and return
 <var>promise</var>.

 <li><p>Let <var>resize</var> be false.

 <li><p>Let <var>docs</var> be the result of
 <a lt="collect documents to unfullscreen">collecting documents to unfullscreen</a> given
 <var>doc</var>.
 <!-- cross-process -->

 <li><p>Let <var>topLevelDoc</var> be <var>doc</var>'s <a>node navigable</a>'s
 <a for=navigable>top-level traversable</a>'s <a for=navigable>active document</a>.
 <!-- cross-process -->

 <li><p>If <var>topLevelDoc</var> is in <var>docs</var>, and it is a
 <a>simple fullscreen document</a>, then set <var>doc</var> to <var>topLevelDoc</var> and
 <var>resize</var> to true.

 <li><p>If <var>doc</var>'s <a>fullscreen element</a> is not <a>connected</a>:
  <ol>
   <li><p><a for=set>Append</a> ({{fullscreenchange}}, <var>doc</var>'s <a>fullscreen element</a>)
   to <var>doc</var>'s <a>list of pending fullscreen events</a>.

   <li><p><a lt="unfullscreen an element">Unfullscreen</a> <var>doc</var>'s <a>fullscreen
   element</a>.
  </ol>

 <li><p>Return <var>promise</var>, and run the remaining steps <a>in parallel</a>.

 <li><p>Run the [=fully unlock the screen orientation steps=] with <var>doc</var>.

 <li><p>If <var>resize</var> is true, resize <var>doc</var>'s viewport to its "normal" dimensions.

 <li><p>If <var>doc</var>'s <a>fullscreen element</a> is null, then resolve <var>promise</var> with
 undefined and terminate these steps.

 <li><p>Let <var>exitDocs</var> be the result of
 <a lt="collect documents to unfullscreen">collecting documents to unfullscreen</a> given
 <var>doc</var>.
 <!-- cross-process -->

 <li><p>Let <var>descendantDocs</var> be an <a>ordered set</a> consisting of <var>doc</var>'s
 <a for=Document>descendant navigables</a>' <a for=navigable>active documents</a> whose
 <a>fullscreen element</a> is non-null, if any, in <a>tree order</a>.
 <!-- cross-process -->

 <li>
  <p><a>For each</a> <var>exitDoc</var> in <var>exitDocs</var>:

  <ol>
   <li><p><a for=set>Append</a> ({{fullscreenchange}}, <var>exitDoc</var>'s
   <a>fullscreen element</a>) to <var>exitDoc</var>'s <a>list of pending fullscreen events</a>.

   <li><p>If <var>resize</var> is true, <a lt="unfullscreen a document">unfullscreen
   <var>exitDoc</var></a>.

   <li><p>Otherwise, <a lt="unfullscreen an element">unfullscreen</a> <var>exitDoc</var>'s
   <a>fullscreen element</a>.
  </ol>

 <li>
  <p><a>For each</a> <var>descendantDoc</var> in <var>descendantDocs</var>:

  <ol>
   <li><p><a for=set>Append</a> ({{fullscreenchange}}, <var>descendantDoc</var>'s
   <a>fullscreen element</a>) to <var>descendantDoc</var>'s
   <a>list of pending fullscreen events</a>.

   <li><p><a lt="unfullscreen a document">Unfullscreen <var>descendantDoc</var></a>.
  </ol>

 <p class=note>The order in which documents are <a lt="unfullscreen a document">unfullscreened</a>
 is not observable, because <a>run the fullscreen steps</a> is invoked in <a>tree order</a>.

 <li><p>Resolve <var>promise</var> with undefined.
</ol>
</div>

<p>The <dfn method for=Document><code>exitFullscreen()</code></dfn> method steps are to return the
result of running <a>exit fullscreen</a> on <a>this</a>.

<hr>

<p>The following are the <a>event handlers</a> (and their corresponding
<a>event handler event types</a>) that must be supported by {{Element}} and {{Document}} objects as
<a>event handler IDL attributes</a>:

<table>
 <thead>
  <tr>
   <th><a lt="event handlers">event handler</a>
   <th><a>event handler event type</a>
 <tbody>
  <tr>
   <td><dfn attribute for=Document,Element id=handler-document-onfullscreenchange><code>onfullscreenchange</code></dfn>
   <td><dfn event for=Document,Element><code>fullscreenchange</code></dfn>
  <tr>
   <td><dfn attribute for=Document,Element id=handler-document-onfullscreenerror><code>onfullscreenerror</code></dfn>
   <td><dfn event for=Document,Element><code>fullscreenerror</code></dfn>
</table>

<p class=note>These are not supported by {{ShadowRoot}} or {{Window}} objects, and there are no
corresponding <a>event handler content attributes</a> for {{Element}} objects in any namespace.



<h2 id=ui>UI</h2>

<p>User agents are encouraged to implement native media fullscreen controls in terms of
{{Element/requestFullscreen()}} and {{Document/exitFullscreen()}}.

<p>If the end user instructs the user agent to end a fullscreen session initiated via
{{Element/requestFullscreen()}}, <a>fully exit fullscreen</a> given the
<a for=/>top-level traversable</a>'s <a>active document</a>.

<p>The user agent may end any fullscreen session without instruction from the end user
or call to {{Document/exitFullscreen()}} whenever the user agent deems it necessary.



<h2 id=rendering>Rendering</h2>

<p>This section is to be interpreted equivalently to the Rendering section of HTML. [[!HTML]]


<h3 id=:fullscreen-pseudo-class><code>:fullscreen</code> pseudo-class</h3>

<p>The <dfn id=css-pc-fullscreen selector><code>:fullscreen</code></dfn> pseudo-class must match any
<a>element</a> <var>element</var> for which one of the following conditions is true:

<ul>
 <li><p><var>element</var>'s <a>fullscreen flag</a> is set.

 <li><p><var>element</var> is a <a>shadow host</a> and the result of <a>retargeting</a> its
 <a>node document</a>'s <a>fullscreen element</a> against <var>element</var> is <var>element</var>.
</ul>

<p class="note no-backref">This makes it different from the
{{DocumentOrShadowRoot/fullscreenElement}} API, which returns the topmost <a>fullscreen element</a>.

<h3 id=user-agent-level-style-sheet-defaults>User-agent level style sheet defaults</h3>
<!-- HTML's "The CSS user agent style sheet and presentational hints" section uses this term -->

<pre class=css>
@namespace "http://www.w3.org/1999/xhtml";

*|*:not(:root):fullscreen {
  position:fixed !important;
  inset:0 !important;
  margin:0 !important;
  box-sizing:border-box !important;
  min-width:0 !important;
  max-width:none !important;
  min-height:0 !important;
  max-height:none !important;
  width:100% !important;
  height:100% !important;
  transform:none !important;

  /* intentionally not !important */
  object-fit:contain;
}

iframe:fullscreen {
  border:none !important;
  padding:0 !important;
}

*|*:not(:root):fullscreen::backdrop {
  background:black;
}
</pre>



<h2 id=permissions-policy-integration oldids=feature-policy-integration>Permissions Policy
Integration</h2>

<p>This specification defines a <a>policy-controlled feature</a> identified by the string
"<code><dfn data-lt="fullscreen-feature">fullscreen</dfn></code>". Its <a>default allowlist</a> is
<code>'self'</code>.

<div class="note">
<p>A <a>document</a>'s <a for=Document>permissions policy</a> determines whether any content in that
document is allowed to go fullscreen. If disabled in any document, no content in the document will
be <a>allowed to use</a> fullscreen.

<p>The <{iframe/allowfullscreen}> attribute of the HTML <{iframe}> element affects the <a>container
policy</a> for any document nested in that iframe. Unless overridden by the <{iframe/allow}>
attribute, setting <{iframe/allowfullscreen}> on an iframe is equivalent to <code>&lt;iframe
allow="fullscreen *"&gt;</code>, as described in
[[permissions-policy#iframe-allowfullscreen-attribute]].
</div>



<h2 id=security-and-privacy-considerations>Security and Privacy Considerations</h2>

<p>User agents should ensure, e.g. by means of an overlay, that the end user is aware something is
displayed fullscreen. User agents should provide a means of exiting fullscreen that always works and
advertise this to the user. This is to prevent a site from spoofing the end user by recreating the
user agent or even operating system environment when fullscreen. See also the definition of
{{Element/requestFullscreen()}}.

<p>To enable content in a <a>child navigable</a> to go fullscreen, it needs to be specifically
allowed via permissions policy, either through the <{iframe/allowfullscreen}> attribute of the HTML
<{iframe}> element, or an appropriate declaration in the <{iframe/allow}> attribute of the HTML
<{iframe}> element, or through a `<a http-header><code>Permissions-Policy</code></a>` HTTP header
delivered with the <a>document</a> through which it is nested.

<p>This prevents e.g. content from third parties to go fullscreen without explicit permission.



<h2 id=old-links class=no-num oldids="new-stacking-layer, top-layer, top-layer-add, ::backdrop-pseudo-element, css-pe-backdrop">Previously-hosted definitions</h2>

This specification previously hosted the definitions of <a selector>::backdrop</a>
and the concept of the document's <a>top layer</a>.



<h2 id=acknowledgments class=no-num>Acknowledgments</h2>

<p>Many thanks to Robert O'Callahan for designing the initial model and being awesome.
<!-- https://wiki.mozilla.org/Gecko:FullScreenAPI -->

<p>Thanks to
Andy Earnshaw,
Changwan Hong,
Chris Pearce,
Darin Fisher,
Dave Tapuska,
<i>fantasai</i>,
Giuseppe Pascale,
Glenn Maynard,
Ian Clelland,
Ian Hickson,
Ignacio Solla,
João Eiras,
Josh Soref,
Kagami Sascha Rosylight,
Matt Falkenhagen,
Mihai Balan,
Mounir Lamouri,
Øyvind Stenhaug,
Pat Ladd,
Rafał Chłodnicki,
Riff Jiang,
Rune Lillesveen,
Sigbjørn Vik,
Simon Pieters,
Tab Atkins-Bittner,
Takayoshi Kochi,
Theresa O'Connor,
triple-underscore,
Vincent Scheib, and
Xidorn Quan
for also being awesome.

<p>This standard is edited by <a lang=sv href=https://foolip.org/>Philip Jägenstedt</a>
(<a href=https://google.com/>Google</a>,
<a href=mailto:philip@foolip.org>philip@foolip.org</a>). It was originally written by
<a lang=nl href=https://annevankesteren.nl/>Anne van Kesteren</a>
(<a href=https://www.apple.com/>Apple</a>, <a href=mailto:annevk@annevk.nl>annevk@annevk.nl</a>).
<a lang=tr href=http://tantek.com/>Tantek Çelik</a>
(<a class="p-org org h-org h-card" href=https://www.mozilla.org/>Mozilla</a>,
<a href=mailto:tantek@cs.stanford.edu>tantek@cs.stanford.edu</a>) sorted out legal hassles.