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<!doctype html><html lang="en">
<head>
<meta content="text/html; charset=utf-8" http-equiv="Content-Type">
<title>CSS Transitions Level 2</title>
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<body class="h-entry">
<div class="head">
<p data-fill-with="logo"><a class="logo" href="http://www.w3.org/"> <img alt="W3C" height="48" src="https://www.w3.org/Icons/w3c_home" width="72"> </a> </p>
<h1 class="p-name no-ref" id="title">CSS Transitions Level 2</h1>
<h2 class="no-num no-toc no-ref heading settled" id="subtitle"><span class="content">Editor’s Draft, <time class="dt-updated" datetime="2015-09-30">30 September 2015</time></span></h2>
<div data-fill-with="spec-metadata">
<dl>
<dt>This version:
<dd><a class="u-url" href="http://dev.w3.org/csswg/css-transitions-2/">http://dev.w3.org/csswg/css-transitions-2/</a>
<dt>Feedback:
<dd><span><a href="mailto:www-style@w3.org?subject=%5Bcss-transitions-2%5D%20YOUR%20TOPIC%20HERE">www-style@w3.org</a> with subject line “<kbd>[css-transitions-2] <var>… message topic …</var></kbd>” (<a href="http://lists.w3.org/Archives/Public/www-style/" rel="discussion">archives</a>)</span>
<dt>Issue Tracking:
<dd><a href="https://www.w3.org/Bugs/Public/buglist.cgi?query_format=advanced&amp;product=CSS&amp;component=Transitions&amp;resolution=---">Bugzilla bugs for all levels</a>
<dd><a href="https://github.com/w3c/csswg-drafts/issues/">GitHub</a>
<dd><a href="#issues-index">Inline In Spec</a>
<dt class="editor">Editor:
<dd class="editor p-author h-card vcard"><a class="p-name fn u-email email" href="mailto:dbaron@dbaron.org">L. David Baron</a> (<span class="p-org org">Mozilla</span>)
</dl>
</div>
<div data-fill-with="warning"></div>
<p class="copyright" data-fill-with="copyright"><a href="http://www.w3.org/Consortium/Legal/ipr-notice#Copyright">Copyright</a> © 2015 <a href="http://www.w3.org/"><abbr title="World Wide Web Consortium">W3C</abbr></a><sup>®</sup> (<a href="http://www.csail.mit.edu/"><abbr title="Massachusetts Institute of Technology">MIT</abbr></a>, <a href="http://www.ercim.eu/"><abbr title="Europe
93CD
an Research Consortium for Informatics and Mathematics">ERCIM</abbr></a>, <a href="http://www.keio.ac.jp/">Keio</a>, <a href="http://ev.buaa.edu.cn/">Beihang</a>). W3C <a href="http://www.w3.org/Consortium/Legal/ipr-notice#Legal_Disclaimer">liability</a>, <a href="http://www.w3.org/Consortium/Legal/ipr-notice#W3C_Trademarks">trademark</a> and <a href="http://www.w3.org/Consortium/Legal/copyright-documents">document use</a> rules apply. </p>
<hr title="Separator for header">
</div>
<h2 class="no-num no-toc no-ref heading settled" id="abstract"><span class="content">Abstract</span></h2>
<div class="p-summary" data-fill-with="abstract">
<p>CSS Transitions allows property changes in CSS values to occur smoothly over a specified duration.</p>
<a href="http://www.w3.org/TR/CSS/">CSS</a> is a language for describing the rendering of structured documents
(such as HTML and XML)
on screen, on paper, in speech, etc.
</div>
<h2 class="no-num no-toc no-ref heading settled" id="status"><span class="content">Status of this document</span></h2>
<div data-fill-with="status">
<p> This is a public copy of the editors’ draft.
It is provided for discussion only and may change at any moment.
Its publication here does not imply endorsement of its contents by W3C.
Don’t cite this document other than as work in progress. </p>
<p> The (<a href="http://lists.w3.org/Archives/Public/www-style/">archived</a>) public mailing list <a href="mailto:www-style@w3.org?Subject=%5Bcss-transitions-2%5D%20PUT%20SUBJECT%20HERE">www-style@w3.org</a> (see <a href="http://www.w3.org/Mail/Request">instructions</a>)
is preferred for discussion of this specification.
When sending e-mail,
please put the text “css-transitions-2” in the subject,
preferably like this:
“[css-transitions-2] <em>…summary of comment…</em>” </p>
<p> This document was produced by the <a href="http://www.w3.org/Style/CSS/members">CSS Working Group</a> (part of the <a href="http://www.w3.org/Style/">Style Activity</a>). </p>
<p> This document was produced by a group operating under
the <a href="http://www.w3.org/Consortium/Patent-Policy-20040205/">5 February 2004 W3C Patent Policy</a>.
W3C maintains a <a href="http://www.w3.org/2004/01/pp-impl/32061/status" rel="disclosure">public list of any patent disclosures</a> 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 <a href="http://www.w3.org/Consortium/Patent-Policy-20040205/#def-essential">Essential Claim(s)</a> must disclose the information in accordance with <a href="http://www.w3.org/Consortium/Patent-Policy-20040205/#sec-Disclosure">section 6 of the W3C Patent Policy</a>. </p>
<p> This document is governed by the <a href="http://www.w3.org/2015/Process-20150901/" id="w3c_process_revision">1 September 2015 W3C Process Document</a>. </p>
<p></p>
</div>
<div data-fill-with="at-risk"></div>
<h2 class="no-num no-toc no-ref heading settled" id="contents"><span class="content">Table of Contents</span></h2>
<div data-fill-with="table-of-contents" role="navigation">
<ul class="toc" role="directory">
<li><a href="#delta"><span class="secno">1</span> <span class="content">Delta specification</span></a>
<li>
<a href="#starting"><span class="secno">2</span> <span class="content">Starting of transitions</span></a>
<ul class="toc">
<li><a href="#transition-property-name"><span class="secno">2.1</span> <span class="content">The transition property name</span></a>
<li><a href="#owning-element-section"><span class="secno">2.2</span> <span class="content">Owning element</span></a>
<li><a href="#animation-composite-order"><span class="secno">2.3</span> <span class="content">Animation composite order</span></a>
</ul>
<li>
<a href="#transition-events"><span class="secno">3</span> <span class="content">Transition Events</span></a>
<ul class="toc">
<li><a href="#transition-event-types"><span class="secno">3.1</span> <span class="content">Types of <code>TransitionEvent</code></span></a>
</ul>
<li>
<a href="#interface-dom"><span class="secno">4</span> <span class="content">DOM Interfaces</span></a>
<ul class="toc">
<li><a href="#the-CSSTransition-interface"><span class="secno">4.1</span> <span class="content">The CSSTransition interface</span></a>
<li><a href="#requirements-on-pending-style-changes"><span class="secno">4.2</span> <span class="content">Requirements on pending style changes</span></a>
</ul>
<li><a href="#issues-common"><span class="secno">5</span> <span class="content">Issues commonly raised as issues with previous levels</span></a>
<li><a href="#issues-spec"><span class="secno">6</span> <span class="content">Issues deferred from previous levels of the spec</span></a>
<li>
<a href="#conformance"><span class="secno"></span> <span class="content"> Conformance</span></a>
<ul class="toc">
<li><a href="#conventions"><span class="secno"></span> <span class="content"> Document conventions</span></a>
<li><a href="#conformance-classes"><span class="secno"></span> <span class="content"> Conformance classes</span></a>
<li><a href="#partial"><span class="secno"></span> <span class="content"> Partial implementations</span></a>
<li><a href="#experimental"><span class="secno"></span> <span class="content"> Experimental implementations</span></a>
<li><a href="#testing"><span class="secno"></span> <span class="content"> Non-experimental implementations</span></a>
</ul>
<li>
<a href="#index"><span class="secno"></span> <span class="content">Index</span></a>
<ul class="toc">
<li><a href="#index-defined-here"><span class="secno"></span> <span class="content">Terms defined by this specification</span></a>
<li><a href="#index-defined-elsewhere"><span class="secno"></span> <span class="content">Terms defined by reference</span></a>
</ul>
<li>
<a href="#references"><span class="secno"></span> <span class="content">References</span></a>
<ul class="toc">
<li><a href="#normative"><span class="secno"></span> <span class="content">Normative References</span></a>
</ul>
<li><a href="#idl-index"><span class="secno"></span> <span class="content">IDL Index</span></a>
<li><a href="#issues-index"><span class="secno"></span> <span class="content">Issues Index</span></a>
</ul>
</div>
<main>
<h2 class="heading settled" data-level="1" id="delta"><span class="secno">1. </span><span class="content">Delta specification</span><a class="self-link" href="#delta"></a></h2>
<p>This is a delta specification, meaning that it currently contains
only the differences from CSS Transitions Level 1 <a data-link-type="biblio" href="#biblio-css3-transitions">[CSS3-TRANSITIONS]</a>.
Once the Level 1 specification is closer to complete, it will be merged
with the additions here into a complete level 2 specification.</p>
<h2 class="heading settled" data-level="2" id="starting"><span class="secno">2. </span><span class="content">Starting of transitions</span><a class="self-link" href="#starting"></a></h2>
<p>Associated with each top-level browsing context is a <dfn data-dfn-type="dfn" data-noexport="" id="current-transition-generation">current transition
generation<a class="self-link" href="#current-transition-generation"></a></dfn> that is incremented on each <a data-link-type="dfn" href="https://drafts.csswg.org/css-transitions-1/#style-change-event">style change event</a>.</p>
<p>Each time a new transition is generated, the current value of the (already
incremented) <a data-link-type="dfn" href="#current-transition-generation">current transition generation</a> is stored as the
transition’s <dfn data-dfn-type="dfn" data-noexport="" id="transition-generation">transition generation<a class="self-link" href="#transition-generation"></a></dfn>.</p>
<h3 class="heading settled" data-level="2.1" id="transition-property-name"><span class="secno">2.1. </span><span class="content">The transition property name</span><a class="self-link" href="#transition-property-name"></a></h3>
<p>Although the <a class="property" data-link-type="propdesc" href="https://drafts.csswg.org/css-transitions-1/#propdef-transition-property">transition-property</a> may specify shorthand properties and the <a class="css" data-link-type="maybe" href="https://drafts.csswg.org/css-transitions-1/#valdef-transition-property-all">all</a> keyword, individual transitions are generated for each longhand
sub-property that is animatable. The <dfn data-dfn-type="dfn" data-noexport="" id="expanded-transition-property-name">expanded transition property
name<a class="self-link" href="#expanded-transition-property-name"></a></dfn> of a transition is the name of the longhand sub-property for which
the transition was generated (e.g. <a class="property" data-link-type="propdesc" href="https://drafts.csswg.org/css-backgrounds-3/#border-left-width">border-left-width</a>).</p>
<h3 class="heading settled" data-level="2.2" id="owning-element-section"><span class="secno">2.2. </span><span class="content">Owning element</span><a class="self-link" href="#owning-element-section"></a></h3>
<p>The <dfn data-dfn-type="dfn" data-noexport="" id="owning-element">owning element<a class="self-link" href="#owning-element"></a></dfn> of a transition refers to the element or
pseudo-element to which the <a class="property" data-link-type="propdesc" href="https://drafts.csswg.org/css-transitions-1/#propdef-transition-property">transition-property</a> property was applied that
generated the animation.</p>
<p>If a transition was generated directly by script (e.g. using the <code class="idl"><a data-link-type="idl" href="#csstransition">CSSTransition</a></code> constructor) then it has no <a data-link-type="dfn" href="#owning-element">owning element</a>.</p>
<p>If a transition generated using the markup defined in this specification is
later disassociated from that markup because it is cancelled or replaced by
a newer transition, the animation is disassociated from its <a data-link-type="dfn" href="#owning-element">owning
element</a> (that is, it has no <a data-link-type="dfn" href="#owning-element">owning element</a> from that point
forwards).</p>
<p class="issue" id="issue-bdbc8bc0"><a class="self-link" href="#issue-bdbc8bc0"></a> Define the above more precisely once we rewrite firing of transitions
in terms of Web Animations concepts (specifically when we spell out when we
cancel an animation).</p>
<h3 class="heading settled" data-level="2.3" id="animation-composite-order"><span class="secno">2.3. </span><span class="content">Animation composite order</span><a class="self-link" href="#animation-composite-order"></a></h3>
<p><a data-link-type="dfn" href="https://w3c.github.io/web-animations/#animation">Animations</a> generated from the markup and
interfaces (e.g. the <code class="idl"><a data-link-type="idl" href="#csstransition">CSSTransition</a></code> constructor) defined in this
specification have an <a data-link-type="dfn" href="https://w3c.github.io/web-animations/#animation-type">animation type</a> of ‘CSS Transition’.</p>
<p>CSS Transitions have an <em>earlier</em> composite order that CSS Animations
and animations without a specific <a data-link-type="dfn" href="https://w3c.github.io/web-animations/#animation-type">animation type</a>.</p>
<p>Within the set of CSS Transitions, two animations <var>A</var> and <var>B</var> are sorted in composite order (first to last) as follows:</p>
<ol>
<li data-md="">
<p>If neither <var>A</var> nor <var>B</var> has an <a data-link-type="dfn" href="#owning-element">owning element</a>,
sort based on their relative position in the <a data-link-type="dfn" href="https://w3c.github.io/web-animations/#global-animation-list">global animation list</a>.</p>
<li data-md="">
<p>Otherwise, if only one of <var>A</var> or <var>B</var> has an <a data-link-type="dfn" href="#owning-element">owning
element</a>, let the animation <em>with</em> an <a data-link-type="dfn" href="#owning-element">owning element</a> sort
first.</p>
<li data-md="">
<p>Otherwise, if the <a data-link-type="dfn" href="#owning-element">owning element</a> of <var>A</var> and <var>B</var> differs, sort <var>A</var> and <var>B</var> by <a data-link-type="dfn" href="https://dom.spec.whatwg.org/#concept-tree-order">tree order</a> of their corresponding <a data-link-type="dfn" href="#owning-element">owning elements</a>.
With regard to pseudo-elements, the sort order is as follows:</p>
<ul>
<li data-md="">
<p>element</p>
<li data-md="">
<p>::before</p>
<li data-md="">
<p>::after</p>
<li data-md="">
<p>element children</p>
</ul>
<li data-md="">
<p>Otherwise, if <var>A</var> and <var>B</var> have different <a data-link-type="dfn" href="#transition-generation">transition
generation</a> values, sort by their corresponding <a data-link-type="dfn" href="#transition-generation">transition generation</a> in ascending order.</p>
<li data-md="">
<p>Otherwise, sort <var>A</var> and <var>B</var> in ascending order by the
Unicode codepoints that make up the <a data-link-type="dfn" href="#expanded-transition-property-name">expanded transition property
name</a> of each transition (i.e. without attempting case conversion and
such that ‘-moz-column-width’ sorts before
‘column-width’).</p>
</ol>
<p>Transitions generated using the markup defined in this specification are <em>not</em> added to the <a data-link-type="dfn" href="https://w3c.github.io/web-animations/#global-animation-list">global animation list</a> when they are created.
Instead, these animations are appended to the <a data-link-type="dfn" href="https://w3c.github.io/web-animations/#global-animation-list">global animation list</a> at
the first moment when they transition out of the <a data-link-type="dfn" href="https://w3c.github.io/web-animations/#idle-play-state">idle play state</a> after
being disassociated from their <a data-link-type="dfn" href="#owning-element">owning element</a>.
Transitions that have been disassociated from their <a data-link-type="dfn" href="#owning-element">owning element</a> but are still <a data-link-type="dfn" href="https://w3c.github.io/web-animations/#idle-play-state">idle</a> do not have a defined
composite order.</p>
<p class="note" role="note">Note, this behavior relies on the fact that disassociating a transition
from its <a data-link-type="dfn" href="#owning-element">owning element</a> always causes it to enter (or remain) in the <a data-link-type="dfn" href="https://w3c.github.io/web-animations/#idle-play-state">idle play state</a>.</p>
<p>Transitions created using the <code class="idl"><a data-link-type="idl" href="#csstransition">CSSTransition</a></code> constructor are appended
to the <a data-link-type="dfn" href="https://w3c.github.io/web-animations/#global-animation-list">global animation list</a> at the moment they are constructed.</p>
<h2 class="heading settled" data-level="3" id="transition-events"><span class="secno">3. </span><span class="content">Transition Events</span><a class="self-link" href="#transition-events"></a></h2>
<h3 class="heading settled" data-level="3.1" id="transition-event-types"><span class="secno">3.1. </span><span class="content">Types of <code>TransitionEvent</code></span><a class="self-link" href="#transition-event-types"></a></h3>
<p>The <em>additional</em> types of transition events that can occur are:</p>
<dl>
<dt><dfn class="idl-code" data-dfn-for="transitionevent" data-dfn-type="event" data-export="" id="dom-transitionevent-transitionstart">transitionstart<a class="self-link" href="#dom-transitionevent-transitionstart"></a></dfn>
<dd>
The <a data-link-type="idl" href="#dom-transitionevent-transitionstart">transitionstart</a> event occurs when a transition is started (i.e., when it is added to the set of <a data-link-type="dfn" href="https://drafts.csswg.org/css-transitions-1/#running-transition">running transitions</a>).
<ul>
<li>Bubbles: Yes
<li>Cancelable: No
<li>Context Info: propertyName, elapsedTime, pseudoElement
</ul>
<dt><dfn class="idl-code" data-dfn-for="transitionevent" data-dfn-type="event" data-export="" id="dom-transitionevent-transitioncancel">transitioncancel<a class="self-link" href="#dom-transitionevent-transitioncancel"></a></dfn>
<dd>
The <a data-link-type="idl" href="#dom-transitionevent-transitioncancel">transitioncancel</a> event occurs when a transition is <a data-link-type="dfn" href="https://drafts.csswg.org/css-transitions-1/#cancel">cancelled</a>.
<ul>
<li>Bubbles: Yes
<li>Cancelable: No
<li>Context Info: propertyName, elapsedTime, pseudoElement
</ul>
</dl>
<h2 class="heading settled" data-level="4" id="interface-dom"><span class="secno">4. </span><span class="content">DOM Interfaces</span><a class="self-link" href="#interface-dom"></a></h2>
<h3 class="heading settled" data-level="4.1" id="the-CSSTransition-interface"><span class="secno">4.1. </span><span class="content">The CSSTransition interface</span><a class="self-link" href="#the-CSSTransition-interface"></a></h3>
<pre class="idl">interface <dfn class="idl-code" data-dfn-type="interface" data-export="" id="csstransition">CSSTransition<a class="self-link" href="#csstransition"></a></dfn> : <a data-link-type="idl-name" href="https://w3c.github.io/web-animations/#animation">Animation</a> {
readonly attribute DOMString <a class="idl-code" data-link-type="attribute" data-readonly="" data-type="DOMString " href="#dom-csstransition-transitionproperty">transitionProperty</a>;
};
</pre>
<dl>
<dt data-md="">
<p><dfn class="idl-code" data-dfn-for="CSSTransition" data-dfn-type="attribute" data-export="" id="dom-csstransition-transitionproperty">transitionProperty<a class="self-link" href="#dom-csstransition-transitionproperty"></a></dfn>, <span> of type <a data-link-type="idl-name" href="http://heycam.github.io/webidl/#idl-DOMString">DOMString</a>, readonly</span></p>
<dd data-md="">
<p>The <a data-link-type="dfn" href="#expanded-transition-property-name">expanded transition property name</a> of this transition.</p>
</dl>
<div class="issue" id="issue-861d9310">
<a class="self-link" href="#issue-861d9310"></a>
<p>This int
8096
erface needs a constructor. Perhaps something like the following,</p>
<pre class="idl">[<dfn class="idl-code" data-dfn-for="CSSTransition" data-dfn-type="constructor" data-export="" data-lt="CSSTransition(target, transitionProperty, transitionValue, options)" id="dom-csstransition-csstransition">Constructor<a class="self-link" href="#dom-csstransition-csstransition"></a></dfn> (<a data-link-type="idl-name" href="http://www.w3.org/TR/web-animations/#animatable">Animatable</a>? <dfn class="idl-code" data-dfn-for="CSSTransition/CSSTransition(target, transitionProperty, transitionValue, options)" data-dfn-type="argument" data-export="" id="dom-csstransition-csstransition-target-transitionproperty-transitionvalue-options-target">target<a class="self-link" href="#dom-csstransition-csstransition-target-transitionproperty-transitionvalue-options-target"></a></dfn>,
DOMString <dfn class="idl-code" data-dfn-for="CSSTransition/CSSTransition(target, transitionProperty, transitionValue, options)" data-dfn-type="argument" data-export="" id="dom-csstransition-csstransition-target-transitionproperty-transitionvalue-options-transitionproperty">transitionProperty<a class="self-link" href="#dom-csstransition-csstransition-target-transitionproperty-transitionvalue-options-transitionproperty"></a></dfn>,
any <dfn class="idl-code" data-dfn-for="CSSTransition/CSSTransition(target, transitionProperty, transitionValue, options)" data-dfn-type="argument" data-export="" id="dom-csstransition-csstransition-target-transitionproperty-transitionvalue-options-transitionvalue">transitionValue<a class="self-link" href="#dom-csstransition-csstransition-target-transitionproperty-transitionvalue-options-transitionvalue"></a></dfn>,
optional (unrestricted double or <a data-link-type="idl-name" href="http://www.w3.org/TR/web-animations/#dictdef-keyframeeffectoptions">KeyframeEffectOptions</a>) <dfn class="idl-code" data-dfn-for="CSSTransition/CSSTransition(target, transitionProperty, transitionValue, options)" data-dfn-type="argument" data-export="" id="dom-csstransition-csstransition-target-transitionproperty-transitionvalue-options-options">options<a class="self-link" href="#dom-csstransition-csstransition-target-transitionproperty-transitionvalue-options-options"></a></dfn>),
<dfn class="idl-code" data-dfn-for="CSSTransition" data-dfn-type="constructor" data-export="" data-lt="CSSTransition(target, transitionProperty, transitionValue, options, timeline)" id="dom-csstransition-csstransition-target-transitionproperty-transitionvalue-options-timeline">Constructor<a class="self-link" href="#dom-csstransition-csstransition-target-transitionproperty-transitionvalue-options-timeline"></a></dfn> (<a data-link-type="idl-name" href="http://www.w3.org/TR/web-animations/#animatable">Animatable</a>? <dfn class="idl-code" data-dfn-for="CSSTransition/CSSTransition(target, transitionProperty, transitionValue, options, timeline)" data-dfn-type="argument" data-export="" id="dom-csstransition-csstransition-target-transitionproperty-transitionvalue-options-timeline-target">target<a class="self-link" href="#dom-csstransition-csstransition-target-transitionproperty-transitionvalue-options-timeline-target"></a></dfn>,
DOMString <dfn class="idl-code" data-dfn-for="CSSTransition/CSSTransition(target, transitionProperty, transitionValue, options, timeline)" data-dfn-type="argument" data-export="" id="dom-csstransition-csstransition-target-transitionproperty-transitionvalue-options-timeline-transitionproperty">transitionProperty<a class="self-link" href="#dom-csstransition-csstransition-target-transitionproperty-transitionvalue-options-timeline-transitionproperty"></a></dfn>,
any <dfn class="idl-code" data-dfn-for="CSSTransition/CSSTransition(target, transitionProperty, transitionValue, options, timeline)" data-dfn-type="argument" data-export="" id="dom-csstransition-csstransition-target-transitionproperty-transitionvalue-options-timeline-transitionvalue">transitionValue<a class="self-link" href="#dom-csstransition-csstransition-target-transitionproperty-transitionvalue-options-timeline-transitionvalue"></a></dfn>,
(unrestricted double or <a data-link-type="idl-name" href="http://www.w3.org/TR/web-animations/#dictdef-keyframeeffectoptions">KeyframeEffectOptions</a>) <dfn class="idl-code" data-dfn-for="CSSTransition/CSSTransition(target, transitionProperty, transitionValue, options, timeline)" data-dfn-type="argument" data-export="" id="dom-csstransition-csstransition-target-transitionproperty-transitionvalue-options-timeline-options">options<a class="self-link" href="#dom-csstransition-csstransition-target-transitionproperty-transitionvalue-options-timeline-options"></a></dfn>,
<a data-link-type="idl-name" href="http://www.w3.org/TR/web-animations/#animationtimeline">AnimationTimeline</a>? <dfn class="idl-code" data-dfn-for="CSSTransition/CSSTransition(target, transitionProperty, transitionValue, options, timeline)" data-dfn-type="argument" data-export="" id="dom-csstransition-csstransition-target-transitionproperty-transitionvalue-options-timeline-timeline">timeline<a class="self-link" href="#dom-csstransition-csstransition-target-transitionproperty-transitionvalue-options-timeline-timeline"></a></dfn>)]
partial interface <a class="idl-code" data-link-type="interface" href="#csstransition">CSSTransition</a> { };
</pre>
<p>Using <code>any</code> as the type for <code>transitionValue</code> would allow
the following usage:</p>
<pre class="example lang-javascript" id="example-36ca8d2f"><a class="self-link" href="#example-36ca8d2f"></a>var transition = new CSSTransition(elem, 'opacity', 1, 2000);
transition.play();
</pre>
<p>The above example, however, is <em>not</em> equivalent to triggering a
transition. It has the following differences:</p>
<ul>
<li data-md="">
<p>It does not update the specified style.</p>
<li data-md="">
<p>It would not cancel any existing transition on the given property unless
we add special wording to that effect.</p>
<li data-md="">
<p>It would exhibit different composite order to a regular transition
(this should be easily fixed, however).</p>
<li data-md="">
<p>It has been suggested that <a href="https://github.com/w3c/web-animations/issues/62#issuecomment-117357703">script-generated
animations should not apply to the transition level of the cascade</a>.</p>
</ul>
<p>It is unclear how much we should extend the <code class="idl"><a data-link-type="idl" href="#csstransition">CSSTransition</a></code> constructor to
overcome the above limitations so that it can be used to generate transitions
programmatically, or whether we should introduce a separate helper method such
as has been <a href="https://lists.w3.org/Archives/Public/www-style/2011Mar/0729.html">suggested
elsewhere</a>.</p>
</div>
<h3 class="heading settled" data-level="4.2" id="requirements-on-pending-style-changes"><span class="secno">4.2. </span><span class="content">Requirements on pending style changes</span><a class="self-link" href="#requirements-on-pending-style-changes"></a></h3>
<p>Various operations may affect the <a data-link-type="dfn" href="https://drafts.csswg.org/css-cascade-4/#computed-value">computed values</a> of
properties on elements. User agents may, as an optimization, defer recomputing
these values until it becomes necessary.
However, all operations included in programming interface defined in this
specification, as well as those operations defined in Web Animations <a data-link-type="biblio" href="#biblio-web-animations">[WEB-ANIMATIONS]</a> that may return objects defined by this specification,
must produce a result consistent with having fully processed any such pending
changes to computed values.</p>
<div class="note" role="note">
As an example, in the following code fragment, when the specified value of <code>elem</code>’s <a class="property" data-link-type="propdesc" href="https://drafts.csswg.org/css-color-4/#propdef-opacity">opacity</a> property is updated, a user agent may defer
recalculating the computed value of the <a class="property" data-link-type="propdesc" href="https://drafts.csswg.org/css-animations-1/#propdef-animation">animation</a> property.
<p>The first time this occurs, calling <code class="idl"><a data-link-type="idl" href="https://drafts.csswg.org/cssom-1/#dom-window-getcomputedstyle">getComputedStyle(elt)</a></code> and
subsequently accessing the <code>opacity</code> property of the result will
cause the user agent to recompute the value of opacity.</p>
<p>After the <a class="property" data-link-type="propdesc" href="https://drafts.csswg.org/css-color-4/#propdef-opacity">opacity</a> property is updated a second time, the <code class="idl"><a data-link-type="idl" href="http://www.w3.org/TR/web-animations/#dom-animatable-getanimations">getAnimations()</a></code> method is called on <code>elem</code>.
This method is specified by Web Animations and can return <code class="idl"><a data-link-type="idl" href="#csstransition">CSSTransition</a></code> objects as defined in this specification.
Hence, as result of the requirements in this section, the user agent must apply
any pending style changes thus generating a new <code class="idl"><a data-link-type="idl" href="#csstransition">CSSTransition</a></code> for the <a class="property" data-link-type="propdesc" href="https://drafts.csswg.org/css-color-4/#propdef-opacity">opacity</a> property before returning its result.</p>
<div>
<pre class="example lang-javascript" id="example-e4db8bb0"><a class="self-link" href="#example-e4db8bb0"></a>elem.style.transition = 'opacity 100s';
elem.style.opacity = '0';
window.getComputedStyle(elem).opacity; // 0
elem.style.opacity = '1';
elem.getAnimations()[0].transitionProperty // 'opacity'
</pre>
</div>
</div>
<h2 class="heading settled" data-level="5" id="issues-common"><span class="secno">5. </span><span class="content">Issues commonly raised as issues with previous levels</span><a class="self-link" href="#issues-common"></a></h2>
<p> These issues were commonly reported issues
with the previous level of the specification. </p>
<div class="issue" id="issue-3a621af8">
<a class="self-link" href="#issue-3a621af8"></a>
<p> More powerful timing function syntax
is a common request from developers.
See, for example: <a href="https://lists.w3.org/Archives/Public/www-style/2013Jun/0376.html">2013 message</a> or <a href="https://lists.w3.org/Archives/Public/public-fx/2015JulSep/thread.html#msg34">2015 thread</a>. </p>
</div>
<div class="issue" id="issue-c2a86011">
<a class="self-link" href="#issue-c2a86011"></a>
<p> Developers frequently have to trigger style flushes
in order to force transitions to start.
It would be good to have an API
that would avoid this requirement.
See, for example, <a href="https://lists.w3.org/Archives/Public/www-style/2011Mar/0729.html">2011 proposal</a>. </p>
</div>
<h2 class="heading settled" data-level="6" id="issues-spec"><span class="secno">6. </span><span class="content">Issues deferred from previous levels of the spec</span><a class="self-link" href="#issues-spec"></a></h2>
<p> These issues were in previous levels of the specification,
but may not turn out to be important in this level either. </p>
<div class="issue" id="issue-21a432a0"><a class="self-link" href="#issue-21a432a0"></a> We may ultimately want to support a keypath syntax
for the <a class="property" data-link-type="propdesc" href="https://drafts.csswg.org/css-transitions-1/#propdef-transition-property">transition-property</a> property.
A keypath syntax
would enable different transitions
to be specified
for components of a property.
For example
the blur of a shadow
could have
a different transition
than the color of a shadow. </div>
</main>
<h2 class="no-ref no-num heading settled" id="conformance"><span class="content"> Conformance</span><a class="self-link" href="#conformance"></a></h2>
<h3 class="no-ref heading settled" id="conventions"><span class="content"> Document conventions</span><a class="self-link" href="#conventions"></a></h3>
<p>Conformance requirements are expressed with a combination of
descriptive assertions and RFC 2119 terminology. The key words
F889
"MUST",
"MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT",
"RECOMMENDED", "MAY", and "OPTIONAL" in the normative parts of this
document are to be interpreted as described in RFC 2119.
However, for readability, these words do not appear in all uppercase
letters in this specification. </p>
<p>All of the text of this specification is normative except sections
explicitly marked as non-normative, examples, and notes. <a data-link-type="biblio" href="#biblio-rfc2119">[RFC2119]</a></p>
<p>Examples in this specification are introduced with the words "for example"
or are set apart from the normative text with <code>class="example"</code>,
like this: </p>
<div class="example" id="example-f839f6c8">
<a class="self-link" href="#example-f839f6c8"></a>
<p>This is an example of an informative example.</p>
</div>
<p>Informative notes begin with the word "Note" and are set apart from the
normative text with <code>class="note"</code>, like this: </p>
<p class="note" role="note">Note, this is an informative note.</p>
<p>Advisements are normative sections styled to evoke special attention and are
set apart from other normative text with <code><strong class="advisement"></code>, like
this: <strong class="advisement"> UAs MUST provide an accessible alternative. </strong> </p>
<h3 class="no-ref heading settled" id="conformance-classes"><span class="content"> Conformance classes</span><a class="self-link" href="#conformance-classes"></a></h3>
<p>Conformance to this specification
is defined for three conformance classes: </p>
<dl>
<dt>style sheet
<dd>A <a href="http://www.w3.org/TR/CSS21/conform.html#style-sheet">CSS
style sheet</a>.
<dt>renderer
<dd>A <a href="http://www.w3.org/TR/CSS21/conform.html#user-agent">UA</a> that interprets the semantics of a style sheet and renders
documents that use them.
<dt>authoring tool
<dd>A <a href="http://www.w3.org/TR/CSS21/conform.html#user-agent">UA</a> that writes a style sheet.
</dl>
<p>A style sheet is conformant to this specification
if all of its statements that use syntax defined in this module are valid
according to the generic CSS grammar and the individual grammars of each
feature defined in this module. </p>
<p>A renderer is conformant to this specification
if, in addition to interpreting the style sheet as defined by the
appropriate specifications, it supports all the features defined
by this specification by parsing them correctly
and rendering the document accordingly. However, the inability of a
UA to correctly render a document due to limitations of the device
does not make the UA non-conformant. (For example, a UA is not
required to render color on a monochrome monitor.) </p>
<p>An authoring tool is conformant to this specification
if it writes style sheets that are syntactically correct according to the
generic CSS grammar and the individual grammars of each feature in
this module, and meet all other conformance requirements of style sheets
as described in this module. </p>
<h3 class="no-ref heading settled" id="partial"><span class="content"> Partial implementations</span><a class="self-link" href="#partial"></a></h3>
<p>So that authors can exploit the forward-compatible parsing rules to
assign fallback values, CSS renderers <strong>must</strong> treat as invalid (and <a href="http://www.w3.org/TR/CSS21/conform.html#ignore">ignore
as appropriate</a>) any at-rules, properties, property values, keywords,
and other syntactic constructs for which they have no usable level of
support. In particular, user agents <strong>must not</strong> selectively
ignore unsupported component values and honor supported values in a single
multi-value property declaration: if any value is considered invalid
(as unsupported values must be), CSS requires that the entire declaration
be ignored.</p>
<h3 class="no-ref heading settled" id="experimental"><span class="content"> Experimental implementations</span><a class="self-link" href="#experimental"></a></h3>
<p>To avoid clashes with future CSS features, the CSS2.1 specification
reserves a <a href="http://www.w3.org/TR/CSS21/syndata.html#vendor-keywords">prefixed
syntax</a> for proprietary and experimental extensions to CSS. </p>
<p>Prior to a specification reaching the Candidate Recommendation stage
in the W3C process, all implementations of a CSS feature are considered
experimental. The CSS Working Group recommends that implementations
use a vendor-prefixed syntax for such features, including those in
W3C Working Drafts. This avoids incompatibilities with future changes
in the draft. </p>
<h3 class="no-ref heading settled" id="testing"><span class="content"> Non-experimental implementations</span><a class="self-link" href="#testing"></a></h3>
<p>Once a specification reaches the Candidate Recommendation stage,
non-experimental implementations are possible, and implementors should
release an unprefixed implementation of any CR-level feature they
can demonstrate to be correctly implemented according to spec. </p>
<p>To establish and maintain the interoperability of CSS across
implementations, the CSS Working Group requests that non-experimental
CSS renderers submit an implementation report (and, if necessary, the
testcases used for that implementation report) to the W3C before
releasing an unprefixed implementation of any CSS features. Testcases
submitted to W3C are subject to review and correction by the CSS
Working Group. </p>
<p>Further information on submitting testcases and implementation reports
can be found from on the CSS Working Group’s website at <a href="http://www.w3.org/Style/CSS/Test/">http://www.w3.org/Style/CSS/Test/</a>.
Questions should be directed to the <a href="http://lists.w3.org/Archives/Public/public-css-testsuite">public-css-testsuite@w3.org</a> mailing list. </p>
<h2 class="no-num heading settled" id="index"><span class="content">Index</span><a class="self-link" href="#index"></a></h2>
<h3 class="no-num heading settled" id="index-defined-here"><span class="content">Terms defined by this specification</span><a class="self-link" href="#index-defined-here"></a></h3>
<ul class="indexlist">
<li><a href="#csstransition">CSSTransition</a><span>, in §4.1</span>
<li><a href="#dom-csstransition-csstransition">CSSTransition(target, transitionProperty, transitionValue, options)</a><span>, in §4.1</span>
<li><a href="#dom-csstransition-csstransition-target-transitionproperty-transitionvalue-options-timeline">CSSTransition(target, transitionProperty, transitionValue, options, timeline)</a><span>, in §4.1</span>
<li><a href="#current-transition-generation">current transition
generation</a><span>, in §2</span>
<li><a href="#expanded-transition-property-name">expanded transition property
name</a><span>, in §2.1</span>
<li>
options
<ul>
<li><a href="#dom-csstransition-csstransition-target-transitionproperty-transitionvalue-options-options">argument for CSSTransition/CSSTransition(target, transitionProperty, transitionValue, options)</a><span>, in §4.1</span>
<li><a href="#dom-csstransition-csstransition-target-transitionproperty-transitionvalue-options-timeline-options">argument for CSSTransition/CSSTransition(target, transitionProperty, transitionValue, options, timeline)</a><span>, in §4.1</span>
</ul>
<li><a href="#owning-element">owning element</a><span>, in §2.2</span>
<li>
target
<ul>
<li><a href="#dom-csstransition-csstransition-target-transitionproperty-transitionvalue-options-target">argument for CSSTransition/CSSTransition(target, transitionProperty, transitionValue, options)</a><span>, in §4.1</span>
<li><a href="#dom-csstransition-csstransition-target-transitionproperty-transitionvalue-options-timeline-target">argument for CSSTransition/CSSTransition(target, transitionProperty, transitionValue, options, timeline)</a><span>, in §4.1</span>
</ul>
<li><a href="#dom-csstransition-csstransition-target-transitionproperty-transitionvalue-options-timeline-timeline">timeline</a><span>, in §4.1</span>
<li><a href="#dom-transitionevent-transitioncancel">transitioncancel</a><span>, in §3.1</span>
<li><a href="#transition-generation">transition generation</a><span>, in §2</span>
<li>
transitionProperty
<ul>
<li><a href="#dom-csstransition-transitionproperty">attribute for CSSTransition</a><span>, in §4.1</span>
<li><a href="#dom-csstransition-csstransition-target-transitionproperty-transitionvalue-options-transitionproperty">argument for CSSTransition/CSSTransition(target, transitionProperty, transitionValue, options)</a><span>, in §4.1</span>
<li><a href="#dom-csstransition-csstransition-target-transitionproperty-transitionvalue-options-timeline-transitionproperty">argument for CSSTransition/CSSTransition(target, transitionProperty, transitionValue, options, timeline)</a><span>, in §4.1</span>
</ul>
<li><a href="#dom-transitionevent-transitionstart">transitionstart</a><span>, in §3.1</span>
<li>
transitionValue
<ul>
<li><a href="#dom-csstransition-csstransition-target-transitionproperty-transitionvalue-options-transitionvalue">argument for CSSTransition/CSSTransition(target, transitionProperty, transitionValue, options)</a><span>, in §4.1</span>
<li><a href="#dom-csstransition-csstransition-target-transitionproperty-transitionvalue-options-timeline-transitionvalue">argument for CSSTransition/CSSTransition(target, transitionProperty, transitionValue, options, timeline)</a><span>, in §4.1</span>
</ul>
</ul>
<h3 class="no-num heading settled" id="index-defined-elsewhere"><span class="content">Terms defined by reference</span><a class="self-link" href="#index-defined-elsewhere"></a></h3>
<ul class="indexlist">
<li>
<a data-link-type="biblio" href="#biblio-css-animations-1">[css-animations-1]</a> defines the following terms:
<ul>
<li><a href="https://drafts.csswg.org/css-animations-1/#propdef-animation">animation</a>
</ul>
<li>
<a data-link-type="biblio" href="#biblio-css-backgrounds-3">[css-backgrounds-3]</a> defines the following terms:
<ul>
<li><a href="https://drafts.csswg.org/css-backgrounds-3/#border-left-width">border-left-width</a>
</ul>
<li>
<a data-link-type="biblio" href="#biblio-css-cascade-4">[css-cascade-4]</a> defines the following terms:
<ul>
<li><a href="https://drafts.csswg.org/css-cascade-4/#computed-value">computed value</a>
</ul>
<li>
<a data-link-type="biblio" href="#biblio-css-color-4">[css-color-4]</a> defines the following terms:
<ul>
<li><a href="https://drafts.csswg.org/css-color-4/#propdef-opacity">opacity</a>
</ul>
<li>
<a data-link-type="biblio" href="#biblio-css-transitions-1">[css-transitions-1]</a> defines the following terms:
<ul>
<li><a href="https://drafts.csswg.org/css-transitions-1/#valdef-transition-property-all">all</a>
<li><a href="https://drafts.csswg.org/css-transitions-1/#cancel">cancel</a>
<li><a href="https://drafts.csswg.org/css-transitions-1/#running-transition">running transition</a>
<li><a href="https://drafts.csswg.org/css-transitions-1/#style-change-event">style change event</a>
<li><a href="https://drafts.csswg.org/css-transitions-1/#propdef-transition-property">transition-property</a>
</ul>
<li>
<a data-link-type="biblio" href="#biblio-cssom-1">[cssom]</a> defines the following terms:
<ul>
<li><a href="https://drafts.csswg.org/cssom-1/#dom-window-getcomputedstyle">getComputedStyle(elt)</a>
</ul>
<li>
<a data-link-type="biblio" href="#biblio-dom-ls">[dom-ls]</a> defines the following terms:
<ul>
<li><a href="https://dom.spec.whatwg.org/#concept-tree-order">tree order</a>
</ul>
<li>
<a data-link-type="biblio" href="#biblio-web-animations">[web-animations]</a> defines the following terms:
<ul>
<li><a href="https://w3c.github.io/web-animations/#animation">Animation</a>
<li><a href="https://w3c.github.io/web-animations/#animation">animation</a>
<li><a href="https://w3c.github.io/web-animations/#animation-type">animation type</a>
<li><a href="https://w3c.github.io/web-animations/#global-animation-list">global animation list</a>
<li><a href="https://w3c.github.io/web-animations/#idle-play-state">idle play state</a>
</ul>
<li>
<a data-link-type="biblio" href="#biblio-web-animations-1">[web-animations-1]</a> defines the following terms:
<ul>
<li><a href="http://www.w3.org/TR/web-animations/#animatable">Animatable</a>
<li><a href="http://www.w3.org/TR/web-animations/#animationtimeline">AnimationTimeline</a>
<li><a href="http://www.w3.org/TR/web-animations/#dictdef-keyframeeffectoptions">KeyframeEffectOptions</a>
<li><a href="http://www.w3.org/TR/web-animations/#dom-animatable-getanimations">getAnimations()</a>
</ul>
<li>
<a data-link-type="biblio" href="#biblio-webidl">[WebIDL]</a> defines the following terms:
<ul>
<li><a href="http://heycam.github.io/webidl/#idl-DOMString">DOMString</a>
</ul>
</ul>
<h2 class="no-num heading settled" id="references"><span class="content">References</span><a class="self-link" href="#references"></a></h2>
<h3 class="no-num heading settled" id="normative"><span class="content">Normative References</span><a class="self-link" href="#normative"></a></h3>
<dl>
<dt id="biblio-webidl"><a class="self-link" href="#biblio-webidl"></a>[WebIDL]
<dd>Cameron McCormack; Boris Zbarsky. <a href="http://www.w3.org/TR/WebIDL-1/">WebIDL Level 1</a>. 4 August 2015. WD. URL: <a href="http://www.w3.org/TR/WebIDL-1/">http://www.w3.org/TR/WebIDL-1/</a>
<dt id="biblio-css-animations-1"><a class="self-link" href="#biblio-css-animations-1"></a>[CSS-ANIMATIONS-1]
<dd>CSS Animations Module Level 1 URL: <a href="http://www.w3.org/TR/css3-animations/">http://www.w3.org/TR/css3-animations/</a>
<dt id="biblio-css-backgrounds-3"><a class="self-link" href="#biblio-css-backgrounds-3"></a>[CSS-BACKGROUNDS-3]
<dd>CSS Backgrounds and Borders Module Level 3 URL: <a href="http://www.w3.org/TR/css3-background/">http://www.w3.org/TR/css3-background/</a>
<dt id="biblio-css-cascade-4"><a class="self-link" href="#biblio-css-cascade-4"></a>[CSS-CASCADE-4]
<dd>Elika Etemad; Tab Atkins Jr.. <a href="http://www.w3.org/TR/css-cascade-4/">CSS Cascading and Inheritance Level 4</a>. 8 September 2015. WD. URL: <a href="http://www.w3.org/TR/css-cascade-4/">http://www.w3.org/TR/css-cascade-4/</a>
<dt id="biblio-css-color-4"><a class="self-link" href="#biblio-css-c
1337
olor-4"></a>[CSS-COLOR-4]
<dd>CSS Color Module Level 4 URL: <a href="https://drafts.csswg.org/css-color-4/">https://drafts.csswg.org/css-color-4/</a>
<dt id="biblio-css-transitions-1"><a class="self-link" href="#biblio-css-transitions-1"></a>[CSS-TRANSITIONS-1]
<dd>CSS Transitions Module Level 1 URL: <a href="http://www.w3.org/TR/css3-transitions/">http://www.w3.org/TR/css3-transitions/</a>
<dt id="biblio-css3-transitions"><a class="self-link" href="#biblio-css3-transitions"></a>[CSS3-TRANSITIONS]
<dd>Dean Jackson; et al. <a href="http://www.w3.org/TR/css3-transitions/">CSS Transitions</a>. 19 November 2013. WD. URL: <a href="http://www.w3.org/TR/css3-transitions/">http://www.w3.org/TR/css3-transitions/</a>
<dt id="biblio-cssom"><a class="self-link" href="#biblio-cssom"></a>[CSSOM]
<dd>Simon Pieters; Glenn Adams. <a href="http://www.w3.org/TR/cssom/">CSS Object Model (CSSOM)</a>. 5 December 2013. WD. URL: <a href="http://www.w3.org/TR/cssom/">http://www.w3.org/TR/cssom/</a>
<dt id="biblio-dom-ls"><a class="self-link" href="#biblio-dom-ls"></a>[DOM-LS]
<dd>Document Object Model URL: <a href="https://dom.spec.whatwg.org/">https://dom.spec.whatwg.org/</a>
<dt id="biblio-rfc2119"><a class="self-link" href="#biblio-rfc2119"></a>[RFC2119]
<dd>S. Bradner. <a href="https://tools.ietf.org/html/rfc2119">Key words for use in RFCs to Indicate Requirement Levels</a>. March 1997. Best Current Practice. URL: <a href="https://tools.ietf.org/html/rfc2119">https://tools.ietf.org/html/rfc2119</a>
<dt id="biblio-web-animations"><a class="self-link" href="#biblio-web-animations"></a>[WEB-ANIMATIONS]
<dd>Brian Birtles; et al. <a href="http://www.w3.org/TR/web-animations-1/">Web Animations</a>. 7 July 2015. WD. URL: <a href="http://www.w3.org/TR/web-animations-1/">http://www.w3.org/TR/web-animations-1/</a>
<dt id="biblio-web-animations-1"><a class="self-link" href="#biblio-web-animations-1"></a>[WEB-ANIMATIONS-1]
<dd>Brian Birtles; et al. <a href="http://www.w3.org/TR/web-animations-1/">Web Animations</a>. 7 July 2015. WD. URL: <a href="http://www.w3.org/TR/web-animations-1/">http://www.w3.org/TR/web-animations-1/</a>
</dl>
<h2 class="no-num heading settled" id="idl-index"><span class="content">IDL Index</span><a class="self-link" href="#idl-index"></a></h2>
<pre class="idl">interface <a href="#csstransition">CSSTransition</a> : <a data-link-type="idl-name" href="https://w3c.github.io/web-animations/#animation">Animation</a> {
readonly attribute DOMString <a class="idl-code" data-link-type="attribute" data-readonly="" data-type="DOMString " href="#dom-csstransition-transitionproperty">transitionProperty</a>;
};
[<a href="#dom-csstransition-csstransition">Constructor</a> (<a data-link-type="idl-name" href="http://www.w3.org/TR/web-animations/#animatable">Animatable</a>? <a href="#dom-csstransition-csstransition-target-transitionproperty-transitionvalue-options-target">target</a>,
DOMString <a href="#dom-csstransition-csstransition-target-transitionproperty-transitionvalue-options-transitionproperty">transitionProperty</a>,
any <a href="#dom-csstransition-csstransition-target-transitionproperty-transitionvalue-options-transitionvalue">transitionValue</a>,
optional (unrestricted double or <a data-link-type="idl-name" href="http://www.w3.org/TR/web-animations/#dictdef-keyframeeffectoptions">KeyframeEffectOptions</a>) <a href="#dom-csstransition-csstransition-target-transitionproperty-transitionvalue-options-options">options</a>),
<a href="#dom-csstransition-csstransition-target-transitionproperty-transitionvalue-options-timeline">Constructor</a> (<a data-link-type="idl-name" href="http://www.w3.org/TR/web-animations/#animatable">Animatable</a>? <a href="#dom-csstransition-csstransition-target-transitionproperty-transitionvalue-options-timeline-target">target</a>,
DOMString <a href="#dom-csstransition-csstransition-target-transitionproperty-transitionvalue-options-timeline-transitionproperty">transitionProperty</a>,
any <a href="#dom-csstransition-csstransition-target-transitionproperty-transitionvalue-options-timeline-transitionvalue">transitionValue</a>,
(unrestricted double or <a data-link-type="idl-name" href="http://www.w3.org/TR/web-animations/#dictdef-keyframeeffectoptions">KeyframeEffectOptions</a>) <a href="#dom-csstransition-csstransition-target-transitionproperty-transitionvalue-options-timeline-options">options</a>,
<a data-link-type="idl-name" href="http://www.w3.org/TR/web-animations/#animationtimeline">AnimationTimeline</a>? <a href="#dom-csstransition-csstransition-target-transitionproperty-transitionvalue-options-timeline-timeline">timeline</a>)]
partial interface <a class="idl-code" data-link-type="interface" href="#csstransition">CSSTransition</a> { };
</pre>
<h2 class="no-num heading settled" id="issues-index"><span class="content">Issues Index</span><a class="self-link" href="#issues-index"></a></h2>
<div style="counter-reset:issue">
<div class="issue"> Define the above more precisely once we rewrite firing of transitions
in terms of Web Animations concepts (specifically when we spell out when we
cancel an animation).<a href="#issue-bdbc8bc0"> ↵ </a></div>
<div class="issue">
<p>This interface needs a constructor. Perhaps something like the following,</p>
<pre class="idl">[<span>Constructor</span> (<a data-link-type="idl-name" href="http://www.w3.org/TR/web-animations/#animatable">Animatable</a>? <span>target</span>,
DOMString <span>transitionProperty</span>,
any <span>transitionValue</span>,
optional (unrestricted double or <a data-link-type="idl-name" href="http://www.w3.org/TR/web-animations/#dictdef-keyframeeffectoptions">KeyframeEffectOptions</a>) <span>options</span>),
<span>Constructor</span> (<a data-link-type="idl-name" href="http://www.w3.org/TR/web-animations/#animatable">Animatable</a>? <span>target</span>,
DOMString <span>transitionProperty</span>,
any <span>transitionValue</span>,
(unrestricted double or <a data-link-type="idl-name" href="http://www.w3.org/TR/web-animations/#dictdef-keyframeeffectoptions">KeyframeEffectOptions</a>) <span>options</span>,
<a data-link-type="idl-name" href="http://www.w3.org/TR/web-animations/#animationtimeline">AnimationTimeline</a>? <span>timeline</span>)]
partial interface <a class="idl-code" data-link-type="interface" href="#csstransition">CSSTransition</a> { };
</pre>
<p>Using <code>any</code> as the type for <code>transitionValue</code> would allow
the following usage:</p>
<pre class="example lang-javascript highlight"><span class="kd">var</span> <span class="nx">transition</span> <span class="o">=</span> <span class="k">new</span> <span class="nx">CSSTransition</span><span class="p">(</span><span class="nx">elem</span><span class="p">,</span> <span class="s1">'opacity'</span><span class="p">,</span> <span class="mi">1</span><span class="p">,</span> <span class="mi">2000</span><span class="p">);</span>
<span class="nx">transition</span><span class="p">.</span><span class="nx">play</span><span class="p">();</span></pre>
<p>The above example, however, is <em>not</em> equivalent to triggering a
transition. It has the following differences:</p>
<ul>
<li data-md="">
<p>It does not update the specified style.</p>
<li data-md="">
<p>It would not cancel any existing transition on the given property unless
we add special wording to that effect.</p>
<li data-md="">
<p>It would exhibit different composite order to a regular transition
(this should be easily fixed, however).</p>
<li data-md="">
<p>It has been suggested that <a href="https://github.com/w3c/web-animations/issues/62#issuecomment-117357703">script-generated
animations should not apply to the transition level of the cascade</a>.</p>
</ul>
<p>It is unclear how much we should extend the <code class="idl"><a data-link-type="idl" href="#csstransition">CSSTransition</a></code> constructor to
overcome the above limitations so that it can be used to generate transitions
programmatically, or whether we should introduce a separate helper method such
as has been <a href="https://lists.w3.org/Archives/Public/www-style/2011Mar/0729.html">suggested
elsewhere</a>.</p>
<a href="#issue-861d9310"> ↵ </a>
</div>
<div class="issue">
<p> More powerful timing function syntax
is a common request from developers.
See, for example: <a href="https://lists.w3.org/Archives/Public/www-style/2013Jun/0376.html">2013 message</a> or <a href="https://lists.w3.org/Archives/Public/public-fx/2015JulSep/thread.html#msg34">2015 thread</a>. </p>
<a href="#issue-3a621af8"> ↵ </a>
</div>
<div class="issue">
<p> Developers frequently have to trigger style flushes
in order to force transitions to start.
It would be good to have an API
that would avoid this requirement.
See, for example, <a href="https://lists.w3.org/Archives/Public/www-style/2011Mar/0729.html">2011 proposal</a>. </p>
<a href="#issue-c2a86011"> ↵ </a>
</div>
<div class="issue"> We may ultimately want to support a keypath syntax
for the <a class="property" data-link-type="propdesc" href="https://drafts.csswg.org/css-
3A03
transitions-1/#propdef-transition-property">transition-property</a> property.
A keypath syntax
would enable different transitions
to be specified
for components of a property.
For example
the blur of a shadow
could have
a different transition
than the color of a shadow. <a href="#issue-21a432a0"> ↵ </a></div>
</div>
</body>
</html>