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[css-transitions] Add initial draft of Security Considerations, Privacy Considerations, and Accessibility Considerations.
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‎css-transitions/Overview.bs‎

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@@ -32,6 +32,7 @@ Abstract: CSS Transitions allows property changes in CSS values to occur smoothl
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Status Text: <strong>This document</strong> is expected to be relatively close to last call. While some issues raised have yet to be addressed, new features are extremely unlikely to be considered for this level. <p>The following behaviors are at risk: <ul><li><a href="#discrete-interpolation-at-risk">Interpolation in steps of property types that cannot be interpolated</a></li></ul>
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Ignored Terms: float
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Ignored Vars: x1, x2, y1, y2
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Link Defaults: css-transforms (property) transform
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</pre>
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<!-- FIXME: font-size and font-weight link defaults don't work -->
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<pre class="link-defaults">
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</tr>
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</table> -->
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Security Considerations {#security}
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===================================
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<em>This section is not normative.</em>
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The security implications of this specification are limited
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because it doesn't allow Web content to do things
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that it could not do before.
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Rather, it allows things that could previously be done with script
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to be done declaratively,
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and it ways that implementations can optimize (for frame rate and
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CPU usage).
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One of the major categories of optimizations
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that implementations can make is implementing animation
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of certain high-value properties (such as 'transform' and 'opacity')
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run on a browser's compositor thread or process
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without updating style or layout on the main Web content thread
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unless up-to-date style data are needed.
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This optimization often requires allocations of graphics memory
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to display the contents of the element being animated.
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Implementations should take care to ensure that Web content
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cannot trigger unsafe out-of-memory handling
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by using large numbers of animations
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or animations on elements covering large areas
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(where large may be defined in terms of pre-transform or post-transform size).
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Privacy Considerations {#privacy}
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=================================
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<em>This section is not normative.</em>
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As for security, the privacy considerations of this specification are limited
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because it does not allow Web content to do things that it could not do before.
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This specification may provide additional mechanisms that help to determine
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characteristics of the user's hardware or software.
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However, ability to determine performance characteristics of the user's
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hardware or software is common to many Web technologies,
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and this specification does not introduce new capabilities.
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As described in [[#accessibility]],
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implementations may provide mitigations to help users with disabilities.
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These mitigations are likely to be detectable by Web content,
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which means that users who would benefit from these mitigations
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may face a tradeoff between keeping their disability private from
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the Web content or benefiting from the mitigation.
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Accessibility Considerations {#accessibility}
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=============================================
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<em>This section is not normative.</em>
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Motion {#accessibility-motion}
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------------------------------
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This specification provides declarative mechanisms for animations
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that previously needed to be done using script.
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Providing a declarative mechanism has multiple effects:
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it makes such animations easier to make and thus likely to be more common,
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but it also makes it easier for user agents to modify those animations
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if such modifications are needed to meet a user's accessibility needs.
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Thus, users who are sensitive to movement,
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or who require additional time to read or understand content,
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may benefit from user agent features that allow
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animations to be disabled or slowed down.
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(But see [[#privacy]] for information on the privacy implications
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of such mitigations.)
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User agent implementors should be aware that Web content
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may depend on the firing of <a href="#transition-events">transition events</a>,
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so implementations of such mitigations may wish to fire transition events
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even if the transitions were not run as continuous animations.
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However, it is probably poor practice for Web content to depend on
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such events to function correctly.
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Cascade {#accessibility-cascade}
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--------------------------------
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The CSS <a>cascade</a> is a general mechanism in CSS
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that allows user needs to interact with author styles.
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This specification interacts with the cascade,
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but since it only allows animation between values
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that result from the existing cascade rules,
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it does not interfere with user's ability to force
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CSS properties to have particular values.
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The cascade also allows users to disable transitions entirely
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by overriding the transition properties.
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<h2 id="changes">Changes since Working Draft of 19 November 2013</h2>
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<p>The following are the substantive changes made since the
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<li>Completion of transitions is defined somewhat more precisely.</li>
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<li>The transitionend event is no longer cancelable. This is since it has no default action, so canceling it would have no meaning. It also matches the animation events.</li>
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<li>The interpolation of ''shadow/inset'' values on shadow lists is no longer backwards.</li>
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<li>A [[#conformance]] section and [[#idl-index]] have been added</li>
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<li>A [[#conformance]] section, [[#security]] section, [[#privacy]] section, [[#accessibility]] section, and [[#idl-index]] have been added</li>
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<li>The identifiers accepted by 'transition-property' are defined in terms of <<custom-ident>>.</li>
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<li>Define a little bit more about when changes to computed values happen, by saying at least that implementations must not update the effects of computed values without actually updating computed values.</li>
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</ul>

‎css-transitions/Overview.html‎

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@@ -123,8 +123,16 @@ <h2 class="no-num no-toc no-ref" id="contents">Table of Contents</h2>
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<li><a href="#animatable-css"><span class="secno">8.1</span> <span class="content"><span> Properties from CSS </span></span></a>
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<li><a href="#animatable-svg"><span class="secno">8.2</span> <span class="content"><span> Properties from SVG </span></span></a>
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</ol>
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<li><a href="#changes"><span class="secno">9</span> <span class="content">Changes since Working Draft of 19 November 2013</span></a>
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<li><a href="#acknowledgments"><span class="secno">10</span> <span class="content">Acknowledgments</span></a>
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<li><a href="#security"><span class="secno">9</span> <span class="content">Security Considerations</span></a>
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<li><a href="#privacy"><span class="secno">10</span> <span class="content">Privacy Considerations</span></a>
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<li>
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<a href="#accessibility"><span class="secno">11</span> <span class="content">Accessibility Considerations</span></a>
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<ol class="toc">
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<li><a href="#accessibility-motion"><span class="secno">11.1</span> <span class="content">Motion</span></a>
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<li><a href="#accessibility-cascade"><span class="secno">11.2</span> <span class="content">Cascade</span></a>
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</ol>
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<li><a href="#changes"><span class="secno">12</span> <span class="content">Changes since Working Draft of 19 November 2013</span></a>
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<li><a href="#acknowledgments"><span class="secno">13</span> <span class="content">Acknowledgments</span></a>
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<li>
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<a href="#conformance"><span class="secno"></span> <span class="content"> Conformance</span></a>
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<ol class="toc">
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<h3 class="heading settled" data-level="8.2" id="animatable-svg"><span class="secno">8.2. </span><span class="content"><span id="properties-from-svg-"> Properties from SVG </span></span 5D59 ><a class="self-link" href="#animatable-svg"></a></h3>
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<p> All properties defined as animatable in the SVG specification, provided
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they are one of the property types listed above. </p>
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<h2 class="heading settled" data-level="9" id="changes"><span class="secno">9. </span><span class="content">Changes since Working Draft of 19 November 2013</span><a class="self-link" href="#changes"></a></h2>
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<h2 class="heading settled" data-level="9" id="security"><span class="secno">9. </span><span class="content">Security Considerations</span><a class="self-link" href="#security"></a></h2>
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<p><em>This section is not normative.</em></p>
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<p>The security implications of this specification are limited
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because it doesn’t allow Web content to do things
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that it could not do before.
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Rather, it allows things that could previously be done with script
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to be done declaratively,
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and it ways that implementations can optimize (for frame rate and
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CPU usage).</p>
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<p>One of the major categories of optimizations
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that implementations can make is implementing animation
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of certain high-value properties (such as <a class="property" data-link-type="propdesc" href="https://drafts.csswg.org/css-transforms-1/#propdef-transform">transform</a> and <a class="property" data-link-type="propdesc" href="https://drafts.csswg.org/css-color-3/#opacity">opacity</a>)
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run on a browser’s compositor thread or process
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without updating style or layout on the main Web content thread
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unless up-to-date style data are needed.
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This optimization often requires allocations of graphics memory
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to display the contents of the element being animated.
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Implementations should take care to ensure that Web content
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cannot trigger unsafe out-of-memory handling
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by using large numbers of animations
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or animations on elements covering large areas
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(where large may be defined in terms of pre-transform or post-transform size).</p>
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<h2 class="heading settled" data-level="10" id="privacy"><span class="secno">10. </span><span class="content">Privacy Considerations</span><a class="self-link" href="#privacy"></a></h2>
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<p><em>This section is not normative.</em></p>
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<p>As for security, the privacy considerations of this specification are limited
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because it does not allow Web content to do things that it could not do before.</p>
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<p>This specification may provide additional mechanisms that help to determine
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characteristics of the user’s hardware or software.
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However, ability to determine performance characteristics of the user’s
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hardware or software is common to many Web technologies,
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and this specification does not introduce new capabilities.</p>
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<p>As described in <a href="#accessibility">§11 Accessibility Considerations</a>,
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implementations may provide mitigations to help users with disabilities.
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These mitigations are likely to be detectable by Web content,
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which means that users who would benefit from these mitigations
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may face a tradeoff between keeping their disability private from
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the Web content or benefiting from the mitigation.</p>
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<h2 class="heading settled" data-level="11" id="accessibility"><span class="secno">11. </span><span class="content">Accessibility Considerations</span><a class="self-link" href="#accessibility"></a></h2>
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<p><em>This section is not normative.</em></p>
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<h3 class="heading settled" data-level="11.1" id="accessibility-motion"><span class="secno">11.1. </span><span class="content">Motion</span><a class="self-link" href="#accessibility-motion"></a></h3>
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<p>This specification provides declarative mechanisms for animations
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that previously needed to be done using script.
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Providing a declarative mechanism has multiple effects:
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it makes such animations easier to make and thus likely to be more common,
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but it also makes it easier for user agents to modify those animations
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if such modifications are needed to meet a user’s accessibility needs.</p>
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<p>Thus, users who are sensitive to movement,
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or who require additional time to read or understand content,
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may benefit from user agent features that allow
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animations to be disabled or slowed down.
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(But see <a href="#privacy">§10 Privacy Considerations</a> for information on the privacy implications
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of such mitigations.)</p>
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<p>User agent implementors should be aware that Web content
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may depend on the firing of <a href="#transition-events">transition events</a>,
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so implementations of such mitigations may wish to fire transition events
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even if the transitions were not run as continuous animations.
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However, it is probably poor practice for Web content to depend on
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such events to function correctly.</p>
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<h3 class="heading settled" data-level="11.2" id="accessibility-cascade"><span class="secno">11.2. </span><span class="content">Cascade</span><a class="self-link" href="#accessibility-cascade"></a></h3>
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<p>The CSS <a data-link-type="dfn" href="https://drafts.csswg.org/css-cascade-4/#cascade">cascade</a> is a general mechanism in CSS
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that allows user needs to interact with author styles.
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This specification interacts with the cascade,
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but since it only allows animation between values
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that result from the existing cascade rules,
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it does not interfere with user’s ability to force
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CSS properties to have particular values.</p>
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<p>The cascade also allows users to disable transitions entirely
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by overriding the transition properties.</p>
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<h2 class="heading settled" data-level="12" id="changes"><span class="secno">12. </span><span class="content">Changes since Working Draft of 19 November 2013</span><a class="self-link" href="#changes"></a></h2>
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<p>The following are the substantive changes made since the <a href="https://www.w3.org/TR/2013/WD-css3-transitions-20131119/">Working Draft
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dated 19 November 2013</a>:</p>
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<ul>
@@ -1274,7 +1350,7 @@ <h2 class="heading settled" data-level="9" id="changes"><span class="secno">9. <
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<li>Completion of transitions is defined somewhat more precisely.
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<li>The transitionend event is no longer cancelable. This is since it has no default action, so canceling it would have no meaning. It also matches the animation events.
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<li>The interpolation of <a class="css" data-link-type="maybe" href="https://drafts.csswg.org/css-backgrounds-3/#shadow-inset">inset</a> values on shadow lists is no longer backwards.
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<li>A <a href="#conformance">Conformance</a> section and <a href="#idl-index">IDL Index</a> have been added
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<li>A <a href="#conformance">Conformance</a> section, <a href="#security">§9 Security Considerations</a> section, <a href="#privacy">§10 Privacy Considerations</a> section, <a href="#accessibility">§11 Accessibility Considerations</a> section, and <a href="#idl-index">IDL Index</a> have been added
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<li>The identifiers accepted by <a class="property" data-link-type="propdesc" href="#propdef-transition-property">transition-property</a> are defined in terms of <a class="production css" data-link-type="type" href="https://drafts.csswg.org/css-values-3/#identifier-value">&lt;custom-ident></a>.
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<li>Define a little bit more about when changes to computed values happen, by saying at least that implementations must not update the effects of computed values without actually updating computed values.
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</ul>
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<li>see the <a href="https://www.w3.org/TR/2013/WD-css3-transitions-20130212/ChangeLog">the ChangeLog</a> for changes in previous working drafts
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<li>For more details on these changes, see the version control change logs, which are split in three parts because of file renaming: <a href="https://hg.csswg.org/drafts/log/tip/css-transitions/Overview.bs">change log since 2015 January 26</a>, <a href="https://hg.csswg.org/drafts/log/tip/css-transitions/Overview.src.html">change log from 2013 March 28 to 2015 January 26</a>, <a href="https://hg.csswg.org/drafts/log/tip/css3-transitions/Overview.src.html">change log before 2013 March 28</a>.
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</ol>
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<h2 class="heading settled" data-level="10" id="acknowledgments"><span class="secno">10. </span><span class="content">Acknowledgments</span><a class="self-link" href="#acknowledgments"></a></h2>
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<h2 class="heading settled" data-level="13" id="acknowledgments"><span class="secno">13. </span><span class="content">Acknowledgments</span><a class="self-link" href="#acknowledgments"></a></h2>
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<p>Thanks especially to the feedback from
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Tab Atkins,
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Carine Bournez,
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<a data-link-type="biblio" href="#biblio-css-cascade-4">[css-cascade-4]</a> defines the following terms:
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<ul>
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<li><a href="https://drafts.csswg.org/css-cascade-4/#propdef-all">all</a>
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<li><a href="https://drafts.csswg.org/css-cascade-4/#cascade">cascade</a>
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<li><a href="https://drafts.csswg.org/css-cascade-4/#computed-value">computed value</a>
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<li><a href="https://drafts.csswg.org/css-cascade-4/#valdef-all-inherit">inherit</a>
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<li><a href="https://drafts.csswg.org/css-cascade-4/#valdef-all-initial">initial</a>
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<ul>
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<li><a href="https://drafts.csswg.org/css-text-decor-3/#propdef-text-shadow">text-shadow</a>
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</ul>
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<li>
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<a data-link-type="biblio" href="#biblio-css-transforms-1">[css-transforms-1]</a> defines the following terms:
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<ul>
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<li><a href="https://drafts.csswg.org/css-transforms-1/#propdef-transform">transform</a>
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</ul>
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<li>
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<a data-link-type="biblio" href="#biblio-css-values-3">[css-values]</a> defines the following terms:
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<ul>
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<dd>CSS Color Module Level 3 URL: <a href="https://www.w3.org/TR/css3-color/">https://www.w3.org/TR/css3-color/</a>
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<dt id="biblio-css-text-decor-3"><a class="self-link" href="#biblio-css-text-decor-3"></a>[CSS-TEXT-DECOR-3]
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<dd>Elika Etemad; Koji Ishii. <a href="http://www.w3.org/TR/css-text-decor-3/">CSS Text Decoration Module Level 3</a>. 1 August 2013. CR. URL: <a href="http://www.w3.org/TR/css-text-decor-3/">http://www.w3.org/TR/css-text-decor-3/</a>
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<dt id="biblio-css-transforms-1"><a class="self-link" href="#biblio-css-transforms-1"></a>[CSS-TRANSFORMS-1]
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<dd>Simon Fraser; et al. <a href="http://www.w3.org/TR/css-transforms-1/">CSS Transforms Module Level 1</a>. 26 November 2013. WD. URL: <a href="http://www.w3.org/TR/css-transforms-1/">http://www.w3.org/TR/css-transforms-1/</a>
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<dt id="biblio-css-values"><a class="self-link" href="#biblio-css-values"></a>[CSS-VALUES]
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<dd>Tab Atkins Jr.; Elika Etemad. <a href="http://www.w3.org/TR/css-values/">CSS Values and Units Module Level 3</a>. 11 June 2015. CR. URL: <a href="http://www.w3.org/TR/css-values/">http://www.w3.org/TR/css-values/</a>
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<dt id="biblio-css3-animations"><a class="self-link" href="#biblio-css3-animations"></a>[CSS3-ANIMATIONS]

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