CSS Animations Level 1

Editor’s Draft, 23 November 2014

This version:
http://dev.w3.org/csswg/css3-animations/
Latest version:
http://www.w3.org/TR/css3-animations/
Previous Versions:
http://www.w3.org/TR/2013/WD-css3-animations-20130219/
http://www.w3.org/TR/2012/WD-css3-animations-20120403/
Feedback:
www-style@w3.org with subject line “[css-animations] … message topic …” (archives)
Test Suite:
http://test.csswg.org/suites/css-animations-1_dev/nightly-unstable/
Editors:
(Apple Inc.)
(Mozilla)
Former Editors:
David Hyatt (Apple Inc.)
Chris Marrin (Apple Inc.)
Issues List:
In Bugzilla

Abstract

This CSS module describes a way for authors to animate the values of CSS properties over time, using keyframes. The behavior of these keyframe animations can be controlled by specifying their duration, number of repeats, and repeating behavior.

CSS is a language for describing the rendering of structured documents (such as HTML and XML) on screen, on paper, in speech, etc.

Status of this document

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.

The (archived) public mailing list www-style@w3.org (see instructions) is preferred for discussion of this specification. When sending e-mail, please put the text “css-animations” in the subject, preferably like this: “[css-animations] …summary of comment…

This document was produced by the CSS Working Group (part of the Style Activity).

This document was produced by a group operating under the 5 February 2004 W3C Patent Policy. W3C maintains a public list of any patent disclosures 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 Essential Claim(s) must disclose the information in accordance with section 6 of the W3C Patent Policy.

This document is governed by the 1 August 2014 W3C Process Document.

The following features are at-risk, and may be dropped during the CR period:

Table of Contents

1. Introduction

This section is not normative

CSS Transitions [CSS3-TRANSITIONS] provide a way to interpolate CSS property values when they change as a result of underlying property changes. This provides an easy way to do simple animation, but the start and end states of the animation are controlled by the existing property values, and transitions provide little control to the author on how the animation progresses.

This proposal introduces defined animations, in which the author can specify the changes in CSS properties over time as a set of keyframes. Animations are similar to transitions in that they change the presentational value of CSS properties over time. The principal difference is that while transitions trigger implicitly when property values change, animations are explicitly executed when the animation properties are applied. Because of this, animations require explicit values for the properties being animated. These values are specified using animation keyframes, described below.

Many aspects of the animation can be controlled, including how many times the animation iterates, whether or not it alternates between the begin and end values, and whether or not the animation should be running or paused. An animation can also delay its start time.

2. Values

This specification follows the CSS property definition conventions from [CSS21]. Value types not defined in this specification are defined in CSS Level 2 Revision 1 [CSS21]. Other CSS modules may expand the definitions of these value types: for example [CSS3VAL], when combined with this module, expands the definition of the <length> value type as used in this specification.

In addition to the property-specific values listed in their definitions, all properties defined in this specification also accept the ‘initial’ and ‘inherit’ keyword as their property value. For readability it has not been repeated explicitly.

3. Animations

CSS Animations affect computed property values. This effect happens by adding a specified value to the CSS cascade ([CSS3CASCADE]) (at the level for CSS Animations) that will produce the correct computed value for the current state of the animation. As defined in [CSS3CASCADE], animations override all normal rules, but are overridden by !important rules.

If at one point in time there are multiple animations specifying behavior for the same property, the animation which occurs last in the value of animation-name will override the other animations at that point.

An animation does not affect the computed value before the application of the animation, before the animation delay has expired, and after the end of the animation.

While running, the animation computes the value of those properties it animates. Other values may take precedence over the animated value according to the CSS cascade ([CSS3CASCADE]).

The start time of an animation is the time at which the style applying the animation and the corresponding @keyframes rule are both resolved. If an animation is specified for an element but the corresponding @keyframes rule does not yet exist, the animation cannot start; the animation will start from the beginning as soon as a matching @keyframes rule can be resolved. An animation specified by dynamically modifying the element’s style will start when this style is resolved; that may be immediately in the case of a pseudo style rule such as hover, or may be when the scripting engine returns control to the browser (in the case of style applied by script). Note that dynamically updating keyframe style rules does not start or restart an animation.

An animation applies to an element if its name appears as one of the identifiers in the computed value of the animation-name property and the animation uses a valid @keyframes rule. Once an animation has started it continues until it ends or the animation-name is removed. Changing the values of animation properties while the animation is running has no effect on the amount of time that has elapsed since the animation started running i.e. once the animation is running, updates to animation-delay have no effect. The remainder of the animation runs according to the new animation property values.

Note also that changing the value of animation-name does not necessarily restart an animation (e.g., if a list of animations are applied and one is removed from the list, only that animation will stop; The other animations will continue). In order to restart an animation, it must be removed then reapplied.

The end of the animation is defined by the combination of the animation-duration, animation-iteration-count and animation-fill-mode properties.

div {
  animation-name: diagonal-slide;
  animation-duration: 5s;
  animation-iteration-count: 10;
}

@keyframes diagonal-slide {

  from {
    left: 0;
    top: 0;
  }

  to {
    left: 100px;
    top: 100px;
  }

}

This will produce an animation that moves an element from (0, 0) to (100px, 100px) over five seconds and repeats itself nine times (for a total of ten iterations).

Setting the display property to none will terminate any running animation applied to the element and its descendants. If an element has a display of none, updating display to a value other than none will start all animations applied to the element by the animation-name property, as well as all animations applied to descendants with display other than none.

While authors can use animations to create dynamically changing content, dynamically changing content can lead to seizures in some users. For information on how to avoid content that can lead to seizures, see Guideline 2.3: Seizures: Do not design content in a way that is known to cause seizures ([WCAG20]).

Implementations may ignore animations when the rendering medium is not interactive e.g. when printed. A future version of this specification may define how to render animations for these media.

4. Keyframes

Keyframes are used to specify the values for the animating properties at various points during the animation. The keyframes specify the behavior of one cycle of the animation; the animation may iterate one or more times.

Keyframes are specified using a specialized CSS at-rule. A @keyframes rule consists of the keyword "@keyframes", followed by an identifier giving a name for the animation (which will be referenced using animation-name), followed by a set of style rules (delimited by curly braces).

The keyframe selector for a keyframe style rule consists of a comma-separated list of percentage values or the keywords from or to. The selector is used to specify the percentage along the duration of the animation that the keyframe represents. The keyframe itself is specified by the block of property values declared on the selector. The keyword from is equivalent to the value 0%. The keyword to is equivalent to the value 100%. Note that the percentage unit specifier must be used on percentage values. Therefore, 0 is an invalid keyframe selector.

If a 0% or from keyframe is not specified, then the user agent constructs a 0% keyframe using the computed values of the properties being animated. If a 100% or to keyframe is not specified, then the user agent constructs a 100% keyframe using the computed values of the properties being animated. If a keyframe selector specifies negative percentage values or values higher than 100%, then the keyframe will be ignored.

The keyframe declaration block for a keyframe rule consists of properties and values. The properties defined by this specification are ignored in these rules, with the exception of animation-timing-function, the behavior of which is described below. In addition, keyframe rule declarations qualified with !important are ignored.

The @keyframes rule that is used by an animation will be the last one encountered in sorted rules order that matches the name of the animation specified by the animation-name property.

div {
  animation-name: slide-right;
  animation-duration: 2s;
}

@keyframes slide-right {

  from {
    margin-left: 0px;
  }

  50% {
    margin-left: 110px;
    opacity: 1;
  }

  50% {
     opacity: 0.9;
  }

  to {
    margin-left: 200px;
  }

}

At the 1s mark, the slide-right animation will have the same state as if we had defined the 50% rule like this:

@keyframes slide-right {

  50% {
    margin-left: 110px;
    opacity: 0.9;
  }

  to {
    margin-left: 200px;
  }

}

To determine the set of keyframes, all of the values in the selectors are sorted in increasing order by time. The rules within the @keyframes rule then cascade; the properties of a keyframe may thus derive from more than one @keyframes rule with the same selector value.

If a property is not specified for a keyframe, or is specified but invalid, the animation of that property proceeds as if that keyframe did not exist. Conceptually, it is as if a set of keyframes is constructed for each property that is present in any of the keyframes, and an animation is run independently for each property.

@keyframes wobble {
  0% {
    left: 100px;
  }

  40% {
    left: 150px;
  }

  60% {
    left: 75px;
  }

  100% {
    left: 100px;
  }
}

Four keyframes are specified for the animation named "wobble". In the first keyframe, shown at the beginning of the animation cycle, the value of the left property being animated is 100px. By 40% of the animation duration, left has animated to 150px. At 60% of the animation duration, left has animated back to 75px. At the end of the animation cycle, the value of left has returned to 100px. The diagram below shows the state of the animation if it were given a duration of 10s.

Animation states specified by keyframes

The following is the grammar for the keyframes rule:

keyframes_rule: KEYFRAMES_SYM S+ IDENT S* '{' S* keyframes_blocks '}' S*;

keyframes_blocks: [ keyframe_selector '{' S* declaration? [ ';' S* declaration? ]* '}' S* ]* ;

keyframe_selector: [ FROM_SYM | TO_SYM | PERCENTAGE ] S* [ ',' S* [ FROM_SYM | TO_SYM | PERCENTAGE ] S* ]*;

@{K}{E}{Y}{F}{R}{A}{M}{E}{S}   {return KEYFRAMES_SYM;}
{F}{R}{O}{M}                   {return FROM_SYM;}
{T}{O}                         {return TO_SYM;}

4.1. Timing functions for keyframes

A keyframe style rule may also declare the timing function that is to be used as the animation moves to the next keyframe.

@keyframes bounce {

  from {
    top: 100px;
    animation-timing-function: ease-out;
  }

  25% {
    top: 50px;
    animation-timing-function: ease-in;
  }

  50% {
    top: 100px;
    animation-timing-function: ease-out;
  }

  75% {
    top: 75px;
    animation-timing-function: ease-in;
  }

  to {
    top: 100px;
  }

}

Five keyframes are specified for the animation named "bounce". Between the first and second keyframe (i.e., between 0% and 25%) an ease-out timing function is used. Between the second and third keyframe (i.e., between 25% and 50%) an ease-in timing function is used. And so on. The effect will appear as an element that moves up the page 50px, slowing down as it reaches its highest point then speeding up as it falls back to 100px. The second half of the animation behaves in a similar manner, but only moves the element 25px up the page.

A timing function specified on the to or 100% keyframe is ignored.

See the animation-timing-function property for more information.

4.2. The animation-name property

The animation-name property defines a list of animations that apply. Each name is used to select the keyframe at-rule that provides the property values for the animation. If the name does not match any keyframe at-rule, there are no properties to be animated and the animation will not execute. Furthermore, if the animation name is none then there will be no animation. This can be used to override any animations coming from the cascade. If multiple animations are attempting to modify the same property, then the animation closest to the end of the list of names wins.

Each animation listed by name should have a corresponding value for the other animation properties listed below. If the lists of values for the other animation properties do not have the same length, the length of the animation-name list determines the number of items in each list examined when starting animations. The lists are matched up from the first value: excess values at the end are not used. If one of the other properties doesn’t have enough comma-separated values to match the number of values of animation-name, the UA must calculate its used value by repeating the list of values until there are enough. This truncation or repetition does not affect the computed value.

Note: This is analogous to the behavior of the ‘background-*’properties, with ‘background-image’ analogous to animation-name.

Name:animation-name
Value:<single-animation-name>#
Initial:none
Applies to:all elements, ::before and ::after pseudo-elements
Inherited:none
Percentages:N/A
Media:interactive
Computed value:As specified
Animatable:no
Canonical order:per grammar

<single-animation-name> = none | <custom-ident>

The values of animation-name have the following meanings:

none
No keyframes are specified at all, so there will be no animation. Any other animations properties specified for this animation have no effect.
<custom-ident>
The animation will use the keyframes with the name specified by the <custom-ident>, if they exist.If no such keyframes exist, there is no animation.

The CSS-wide keywords and keywords defined by this property are not valid animation names.

4.3. The animation-duration property

The animation-duration property defines duration of a single animation cycle.

Name:animation-duration
Value:<time>#
Initial:0s
Applies to:all elements, ::before and ::after pseudo-elements
Inherited:no
Percentages:N/A
Media:interactive
Computed value:As specified
Animatable:no
Canonical order:per grammar
<time>
The <time> specifies the length of time that an animation takes to complete one cycle. A negative <time> is invalid.

If the <time> is 0s, like the initial value, the keyframes of the animation have no effect, but the animation itself still occurs instantaneously. Specifically, start and end events are fired; if animation-fill-mode is set to backwards or both, the first frame of the animation, as defined by animation-direction, will be displayed during the animation-delay. Then the last frame of the animation, as defined by animation-direction, will be displayed if animation-fill-mode is set to forwards or both. If animation-fill-mode is set to none then the animation has no visible effect.

4.4. The animation-timing-function property

The animation-timing-function property describes how the animation will progress over one cycle of its duration. See the transition-timing-function property [CSS3-TRANSITIONS] for a complete description of timing function calculation.

Name:animation-timing-function
Value:<single-timing-function>#
Initial:ease
Applies to:all elements, ::before and ::after pseudo-elements
Inherited:no
Percentages:N/A
Media:interactive
Computed value:As specified
Animatable:no
Canonical order:per grammar

The values and meaning of <single-timing-function> are identical to those of <single-transition-timing-function> [CSS3-TRANSITIONS].

The timing function specified applies to each iteration of the animation, not the entire animation in full. For example, if an animation has animation-timing-function: ease-in-out; animation-iteration-count: 2;, it will ease in at the start, ease out as it approaches the end of its first iteration, ease in at the start of its second iteration, and ease out again as it approaches the end of the animation.

When specified in a keyframe, animation-timing-function defines the progression of the animation between the current keyframe and the next keyframe that defines animation-timing-function in sorted keyframe selector order (or the end of the animation if no other keyframe specifies 'animation-timing function'). The specified timing function will apply over this interval independently of the animation’s current direction.

4.5. The animation-iteration-count property

The animation-iteration-count property specifies the number of times an animation cycle is played. The initial value is 1, meaning the animation will play from beginning to end once. This property is often used in conjunction with an animation-direction value of alternate, which will cause the animation to play in reverse on alternate cycles.

The time window during which the animation is active (duration x iteration-count) is known as the active duration.

Name:animation-iteration-count
Value:<single-animation-iteration-count>#
Initial:1
Applies to:all elements, ::before and ::after pseudo-elements
Inherited:no
Percentages:N/A
Media:interactive
Computed value:As specified
Animatable:no
Canonical order:per grammar

<single-animation-iteration-count> = infinite | <number>

infinite
The animation will repeat forever.
<number>

The animation will repeat the specified number of times. If the number is not an integer, the animation will end partway through its last cycle. Negative numbers are invalid.

A value of 0 is valid and, similar to an animation-duration of 0s, causes the animation to occur instantaneously.

If the animation has a duration of 0s, it will occur instantaneously for any valid value of animation-iteration-count, including infinite.

4.6. The animation-direction property

The animation-direction property defines whether or not the animation should play in reverse on some or all cycles. When an animation is played in reverse the timing functions are also reversed. For example, when played in reverse an ease-in animation would appear to be an ease-out animation.

Name:animation-direction
Value:<single-animation-direction>#
Initial:normal
Applies to:all elements, ::before and ::after pseudo-elements
Inherited:no
Percentages:N/A
Media:interactive
Computed value:As specified
Animatable:no
Canonical order:per grammar

<single-animation-direction> = normal | reverse | alternate | alternate-reverse

normal
All iterations of the animation are played as specified.
reverse
All iterations of the animation are played in the reverse direction from the way they were specified.
alternate
The animation cycle iterations that are odd counts are played in the normal direction, and the animation cycle iterations that are even counts are played in a reverse direction.
alternate-reverse
The animation cycle iterations that are odd counts are played in the reverse direction, and the animation cycle iterations that are even counts are played in a normal direction.

Note: For the purpose of determining whether an iteration is even or odd, iterations start counting from 1.

4.7. The animation-play-state property

The animation-play-state property defines whether the animation is running or paused.

Name:animation-play-state
Value:<single-animation-play-state>#
Initial:running
Applies to:all elements, ::before and ::after pseudo-elements
Inherited:no
Percentages:N/A
Media:interactive
Computed value:As specified
Animatable:no
Canonical order:per grammar

<single-animation-play-state> = running | paused

running
While this property is set to running, the animation proceeds as normal.
paused
While this property is set to paused, the animation is paused. The animation continues to apply to the element with the progress it had made before being paused. When unpaused (set back to running), it restarts from where it left off, as if the "clock" that controls the animation had stopped and started again.

If the property is set to paused during the delay phase of the animation, the delay clock is also paused and resumes as soon as animation-play-state is set back to running.

4.8. The animation-delay property

The animation-delay property defines when the animation will start. It allows an animation to begin execution some time after it is applied, or to appear to have begun execution some time before it is applied.

Name:animation-delay
Value:<time>#
Initial:0s
Applies to:all elements, ::before and ::after pseudo-elements
Inherited:no
Percentages:N/A
Media:interactive
Computed value:As specified
Animatable:no
Canonical order:per grammar
<time>
The <time> defines how long of a delay there is between the start of the animation (when the animation is applied to the element via these properties) and when it begins executing. A delay of 0s (the initial value) means that the animation will execute as soon as it is applied.

A negative delay is valid. Similar to a delay of 0s, it means that the animation executes immediately, but is automatically progressed by the absolute value of the delay, as if the animation had started the specified time in the past, and so it appears to start partway through its active duration. If an animation’s keyframes have an implied starting value, the values are taken from the time the animation starts, not some time in the past.

4.9. The animation-fill-mode property

The animation-fill-mode property defines what values are applied by the animation outside the time it is executing. By default, an animation will not affect property values between the time it is applied (the ‘animation-name’ property is set on an element) and the time it begins execution (which is determined by the animation-delay property). Also, by default an animation does not affect property values after the animation ends (determined by the animation-duration and animation-iteration-count properties). The animation-fill-mode property can override this behavior. Dynamic updates to the property will be reflected by property values as needed, whether during the animation delay or after the animation ends.

Name:animation-fill-mode
Value:<single-animation-fill-mode>#
Initial:none
Applies to:all elements, ::before and ::after pseudo-elements
Inherited:no
Percentages:N/A
Media:interactive
Computed value:As specified
Animatable:no
Canonical order:per grammar

<single-animation-fill-mode> = none | forwards | backwards | both

none
The animation has no effect when it is applied but not executing.
forwards
After the animation ends (as determined by its animation-iteration-count), the animation will apply the property values for the time the animation ended. When animation-iteration-count is an integer greater than zero, the values applied will be those for the end of the last completed iteration of the animation (rather than the values for the start of the iteration that would be next). When animation-iteration-count is zero, the values applied will be those that would start the first iteration (just as when animation-fill-mode is backwards).
backwards
During the period defined by animation-delay, the animation will apply the property values defined in the keyframe that will start the first iteration of the animation. These are either the values of the from keyframe (when animation-direction is normal or alternate) or those of the to keyframe (when animation-direction is reverse or alternate-reverse).
both
The effects of both forwards and backwards fill apply.

4.10. The animation shorthand property

The animation shorthand property is a comma-separated list of animation definitions. Each item in the list gives one item of the value for all of the subproperties of the shorthand, which are known as the animation properties. (See the definition of animation-name for what happens when these properties have lists of different lengths, a problem that cannot occur when they are defined using only the animation shorthand.)

Name:animation
Value:<single-animation>#
Initial:see individual properties
Applies to:all elements, ::before and ::after pseudo-elements
Inherited:no
Percentages:N/A
Media:interactive
Computed value:As specified
Animatable:no
Canonical order:per grammar

<single-animation> = <time> || <single-timing-function> || <time> || <single-animation-iteration-count> || <single-animation-direction> || <single-animation-fill-mode> || <single-animation-play-state> || <single-animation-name>

Note that order is important within each animation definition: the first value in each <single-animation> that can be parsed as a <time> is assigned to the animation-duration, and the second value in each <single-animation> that can be parsed as a <time> is assigned to animation-delay.

Note that order is also important within each animation definition for distinguishing <single-animation-name> values from other keywords. When parsing, keywords that are valid for properties other than animation-name whose values were not found earlier in the shorthand must be accepted for those properties rather than for animation-name. Furthermore, when serializing, default values of other properties must be output in at least the cases necessary to distinguish an animation-name that could be a value of another property, and may be output in additional cases.

For example, a value parsed from animation: 3s none backwards (where animation-fill-mode is none and animation-name is backwards) must not be serialized as animation: 3s backwards (where animation-fill-mode is backwards and animation-name is none).

5. Animation Events

Several animation-related events are available through the DOM Event system. The start and end of an animation, and the end of each iteration of an animation, all generate DOM events. An element can have multiple properties being animated simultaneously. This can occur either with a single animation-name value with keyframes containing multiple properties, or with multiple animation-name values. For the purposes of events, each animation-name specifies a single animation. Therefore an event will be generated for each animation-name value and not necessarily for each property being animated.

Any animation for which a valid keyframe rule is defined will run and generate events; this includes animations with empty keyframe rules.

The time the animation has been running is sent with each event generated. This allows the event handler to determine the current iteration of a looping animation or the current position of an alternating animation. This time does not include any time the animation was in the paused play state.

5.1. The AnimationEvent Interface

The AnimationEvent interface provides specific contextual information associated with Animation events.

5.1.1. IDL Definition

[Constructor(DOMString type, optional AnimationEventInit animationEventInitDict)]
interface AnimationEvent : Event {
  readonly attribute DOMString animationName;
  readonly attribute float elapsedTime;
  readonly attribute DOMString pseudoElement;
};
dictionary AnimationEventInit : EventInit {
  DOMString animationName = "";
  float elapsedTime = 0.0;
  DOMString pseudoElement = "";
};

5.1.2. Attributes

animationName, of type , of type DOMString, readonlyDOMString, readonly
The value of the animation-name property of the animation that fired the event.
elapsedTime, of type float, readonly , of type float, readonly
The amount of time the animation has been running, in seconds, when this event fired, excluding any time the animation was paused. For an animationstart event, the elapsedTime is zero unless there was a negative value for animation-delay, in which case the event will be fired with an elapsedTime of (-1 * delay).
pseudoElement, of type , of type DOMString, readonlyDOMString, readonly
The name (beginning with two colons) of the CSS pseudo-element on which the animation runs (in which case the target of the event is that pseudo-element’s corresponding element), or the empty string if the animation runs on an element (which means the target of the event is that element).

AnimationEvent(type, animationEventInitDict) is an event constructor.

5.2. Types of AnimationEvent

The different types of animation events that can occur are:

animationstart
The animationstart event occurs at the start of the animation. If there is an animation-delay then this event will fire once the delay period has expired. A negative delay will cause the event to fire with an elapsedTime equal to the absolute value of the delay; in this case the event will fire whether animation-play-state is set to running or paused.
  • Bubbles: Yes
  • Cancelable: No
  • Context Info: animationName, pseudoElement
animationend
The animationend event occurs when the animation finishes.
  • Bubbles: Yes
  • Cancelable: No
  • Context Info: animationName, elapsedTime, pseudoElement
animationiteration
The animationiteration event occurs at the end of each iteration of an animation, except when an animationend event would fire at the same time. This means that this event does not occur for animations with an iteration count of one or less.
  • Bubbles: Yes
  • Cancelable: No
  • Context Info: animationName, elapsedTime, pseudoElement

6. DOM Interfaces

CSS animations are exposed to the CSSOM through a pair of new interfaces describing the keyframes.

6.1. The CSSRule Interface

The following two rule types are added to the CSSRule interface. They provide identification for the new keyframe and keyframes rules.

6.1.1. IDL Definition

partial interface CSSRule {
    const unsigned short KEYFRAMES_RULE = 7;
    const unsigned short KEYFRAME_RULE = 8;
};

6.2. The CSSKeyframeRule Interface

The CSSKeyframeRule interface represents the style rule for a single key.

6.2.1. IDL Definition

interface CSSKeyframeRule : CSSRule {
           attribute DOMString           keyText;
  readonly attribute CSSStyleDeclaration style;
};

6.2.2. Attributes

keyText, of type , of type DOMStringDOMString
This attribute represents the keyframe selector as a comma-separated list of percentage values. The from and to keywords map to 0% and 100%, respectively.

If keyText is updated with an invalid keyframe selector, a SyntaxError exception must be thrown.

style, of type , of type CSSStyleDeclaration, readonlyCSSStyleDeclaration
This attribute represents the style associated with this keyframe.

6.3. The CSSKeyframesRule Interface

The CSSKeyframesRule interface represents a complete set of keyframes for a single animation.

6.3.1. IDL Definition

interface CSSKeyframesRule : CSSRule {
           attribute DOMString   name;
  readonly attribute CSSRuleList cssRules;

  void            appendRule(DOMString rule);
  void            deleteRule(DOMString key);
  CSSKeyframeRule findRule(DOMString key);
};

6.3.2. Attributes

name, of type , of type DOMStringDOMString
This attribute is the name of the keyframes, used by the animation-name property.

Setting this property to a value matching a CSS-wide keyword or any keyword defined for the animation-name property will throw a SyntaxError exception.

cssRules, of type , of type CSSRuleList, readonlyCSSRuleList
This attribute gives access to the keyframes in the list.

6.3.3. The appendRule method

The appendRule() method appends the passed CSSKeyframeRule at the end of the keyframes rule.

Parameters:

rule of type DOMString
The rule to be appended, expressed in the same syntax as one entry in the @keyframes rule. A valid rule is always appended e.g. even if its key(s) already exists.

No Return Value

No Exceptions

6.3.4. The deleteRule method

The deleteRule() deletes the CSSKeyframeRule with the passed key. If a rule with this key does not exist, the method does nothing.

If multiple rules are specified for the passed key, the last one is deleted.

Parameters:

key of type DOMString
The key which describes the rule to be deleted. A percentage value between 0% and 100%, or one of the keywords from or to which resolve to 0% and 100%, respectively.

No Return Value

No Exceptions

6.3.5. The findRule method

The findRule() returns the rule with a key matching the passed key. If no such rule exists, a null value is returned.

If multiple rules are specified for the passed key, the last one is returned.

Parameters:

key of type DOMString
The key which describes the rule to be deleted. A percentage value between 0% and 100%, or one of the keywords from or to which resolve to 0% and 100%, respectively.

Return Value:

CSSKeyframeRule
The found rule.

No Exceptions

7. Acknowledgements

Thanks especially to the feedback from Tab Atkins, Brian Birtles, Shane Stephens, Carine Bournez, Christian Budde, Anne van Kesteren, Øyvind Stenhaug, Estelle Weyl, and all the rest of the www-style community.

8. Working Group Resolutions that are pending editing

This section is informative and temporary.

The editors are currently behind on editing this spec. The following working group resolutions still need to be edited in:

Conformance

Document conventions

Conformance requirements are expressed with a combination of descriptive assertions and RFC 2119 terminology. The key words "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.

All of the text of this specification is normative except sections explicitly marked as non-normative, examples, and notes. [RFC2119]

Examples in this specification are introduced with the words "for example" or are set apart from the normative text with class="example", like this:

This is an example of an informative example.

Informative notes begin with the word "Note" and are set apart from the normative text with class="note", like this:

Note, this is an informative note.

Advisements are normative sections styled to evoke special attention and are set apart from other normative text with <strong class="advisement">, like this: UAs MUST provide an accessible alternative.

Conformance classes

Conformance to this specification is defined for three conformance classes:

style sheet
A CSS style sheet.
renderer
A UA that interprets the semantics of a style sheet and renders documents that use them.
authoring tool
A UA that writes a style sheet.

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.

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.)

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.

Partial implementations

So that authors can exploit the forward-compatible parsing rules to assign fallback values, CSS renderers must treat as invalid (and ignore as appropriate) any at-rules, properties, property values, keywords, and other syntactic constructs for which they have no usable level of support. In particular, user agents must not 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.

Experimental implementations

To avoid clashes with future CSS features, the CSS2.1 specification reserves a prefixed syntax for proprietary and experimental extensions to CSS.

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.

Non-experimental implementations

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.

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.

Further information on submitting testcases and implementation reports can be found from on the CSS Working Group’s website at http://www.w3.org/Style/CSS/Test/. Questions should be directed to the public-css-testsuite@w3.org mailing list.

References

Normative References

[CSS21]
Bert Bos; et al. Cascading Style Sheets Level 2 Revision 1 (CSS 2.1) Specification. 7 June 2011. W3C Recommendation. URL: http://www.w3.org/TR/2011/REC-CSS2-20110607
[CSS3CASCADE]
Håkon Wium Lie; Elika J. Etemad; Tab Atkins Jr.. CSS Cascading and Inheritance Level 3. 3 October 2013. W3C Candidate Recommendation. (Work in progress.) URL: http://www.w3.org/TR/2013/CR-css-cascade-3-20131003/
[CSS3VAL]
Håkon Wium Lie; Tab Atkins; Elika J. Etemad. CSS Values and Units Module Level 3. 30 July 2013. W3C Candidate Recommendation. (Work in progress.) URL: http://www.w3.org/TR/2013/CR-css3-values-20130730/
[WCAG20]
Ben Caldwell; et al. Web Content Accessibility Guidelines (WCAG) 2.0. 11 December 2008. REC. URL: http://www.w3.org/TR/WCAG20/
[css3-transitions]
Dean Jackson; et al. CSS Transitions. 19 November 2013. WD. URL: http://www.w3.org/TR/css3-transitions/
[rfc2119]
S. Bradner. Key words for use in RFCs to Indicate Requirement Levels. March 1997. Best Current Practice. URL: https://tools.ietf.org/html/rfc2119

Index

Property Index

NameValueInitialApplies toInh.%agesMediaAnimatableCanonical orderComputed value
animation-name<single-animation-name>#noneall elements, ::before and ::after pseudo-elementsnoneN/Ainteractivenoper grammarAs specified
animation-duration<time>#0sall elements, ::before and ::after pseudo-elementsnoN/Ainteractivenoper grammarAs specified
animation-timing-function<single-timing-function>#easeall elements, ::before and ::after pseudo-elementsnoN/Ainteractivenoper grammarAs specified
animation-iteration-count<single-animation-iteration-count>#1all elements, ::before and ::after pseudo-elementsnoN/Ainteractivenoper grammarAs specified
animation-direction<single-animation-direction>#normalall elements, ::before and ::after pseudo-elementsnoN/Ainteractivenoper grammarAs specified
animation-play-state<single-animation-play-state>#runningall elements, ::before and ::after pseudo-elementsnoN/Ainteractivenoper grammarAs specified
animation-delay<time>#0sall elements, ::before and ::after pseudo-elementsnoN/Ainteractivenoper grammarAs specified
animation-fill-mode<single-animation-fill-mode>#noneall elements, ::before and ::after pseudo-elementsnoN/Ainteractivenoper grammarAs specified
animation<single-animation>#see individual propertiesall elements, ::before and ::after pseudo-elementsnoN/Ainteractivenoper grammarAs specified

IDL Index

[Constructor(DOMString type, optional AnimationEventInit animationEventInitDict)]
interface AnimationEvent : Event {
  readonly attribute DOMString animationName;
  readonly attribute float elapsedTime;
  readonly attribute DOMString pseudoElement;
};
dictionary AnimationEventInit : EventInit {
  DOMString animationName = "";
  float elapsedTime = 0.0;
  DOMString pseudoElement = "";
};

partial interface CSSRule {
    const unsigned short KEYFRAMES_RULE = 7;
    const unsigned short KEYFRAME_RULE = 8;
};

interface CSSKeyframeRule : CSSRule {
           attribute DOMString           keyText;
  readonly attribute CSSStyleDeclaration style;
};

interface CSSKeyframesRule : CSSRule {
           attribute DOMString   name;
  readonly attribute CSSRuleList cssRules;

  void            appendRule(DOMString rule);
  void            deleteRule(DOMString key);
  CSSKeyframeRule findRule(DOMString key);
};