Overview.bs

<h1>CSS Animations Level 1</h1>

<pre class='metadata'>
Status: ED
Shortname: css-animations
Level: 1
Group: csswg
TR: http://www.w3.org/TR/css3-animations/
ED: http://dev.w3.org/csswg/css3-animations/
Previous Version: http://www.w3.org/TR/2013/WD-css3-animations-20130219/
Previous Version: http://www.w3.org/TR/2012/WD-css3-animations-20120403/
Editor: Dean Jackson, Apple Inc., dino@apple.com
Editor: L. David Baron, Mozilla, dbaron@dbaron.org
Editor: Sylvain Galineau, Adobe, galineau@adobe.com
Former Editor: David Hyatt, Apple Inc.
Former Editor: Chris Marrin, Apple Inc.

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. 

Ignored Terms: domstring, float, animationeventinit, eventinit, eventtarget, document
</pre>

<h2 id="intro">
Introduction</h2>

	<em>This section is not normative</em>

	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. 

<h2 id="values">
Values</h2>

	 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. 

<h2 id="animations">
Animations</h2>

	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 whose name 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. 

	<figure>
		<img src="./sandwich.png" alt="">
		<figcaption>Computation of animated property values</figcaption>
	</figure>	

	 The diagram above shows how property values are computed. The intrinsic 
	 style is shown at the top of the diagram. The computed value is derived 
	 from intrinsic style at the times when an animation is not running and 
	 also when an animation is delayed (see below for specification of animation 
	 delay). During an animation, the computed style is derived from the 
	 animated value.

	The start time of an animation is the latter of two moments: the time at 
	which the style is resolved that specifies the animation, or the time the 
	document's load event is fired. Therefore, an animation specified in the 
	document style sheet will begin at the document load. An animation specified 
	on an element by modifying the style after the document has loaded will start 
	when the 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).

	An animation applies to an element if its name appears as one of the
	identifiers in the computed value of the 'animation-name' property. Once an 
	animation has started it continues until it ends or the 'animation-name' is 
	removed. The values used for the keyframes and animation properties are 
	snapshotted at the time the animation starts. Changing them during the 
	execution of the animation has no effect. 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 class='example'>
		<pre>
		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;
		  }

		}
		</pre>

		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).

	</div>

	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]]). 

<h2 id="keyframes">
Keyframes</h2>

	 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%’. 
	<span class="note">Note that the percentage unit specifier must be used on percentage values. 
	Therefore, ‘0’ is an invalid keyframe selector.</span>

	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. Properties 
	that are unable to be animated 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. 

	Issue: Need to describe what happens if a property is not present in all keyframes.

	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. @keyframes 
	rules do not cascade; therefore, an animation will never derive keyframes from more than one 
	@keyframes rule.

	Note: Note that since empty @keyframes rule are valid, they may hide the keyframes of those 
	preceding animation definitions with a matching name.

	To determine the set of keyframes, all of the values in the selectors are sorted in increasing order 
	by time. If there are any duplicates, then the last keyframe specified inside the @keyframes rule 
	will be used to provide the keyframe information for that time. There is no cascading within a 
	@keyframes rule if multiple keyframes specify the same keyframe selector values.

	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. 

	<div class='example'>
		<pre>
		@keyframes wobble {
		  0% {
		    left: 100px;
		  }

		  40% {
		    left: 150px;
		  }

		  60% {
		    left: 75px;
		  }

		  100% {
		    left: 100px;
		  }
		}
		</pre>

		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. 

		<figure>
			<img src="./animation1.png" alt="">
			<figcaption>Animation states specified by keyframes</figcaption>
		</figure>	
	</div>

	The following is the grammar for the keyframes rule:

	<pre>
		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;}
	</pre>


<h3 id="timing-funtions">
Timing functions for keyframes</h3>

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

	<div class='example'>
		<pre>
		@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;
		  }

		}
		</pre>

		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. 
	</div>


<h3 id="animation-name">
The 'animation-name' property</h3>

	<pre class='propdef'>
	Name: animation-name
	Value: <<single-animation-name>> [',' <<single-animation-name>>]*
	Initial: none
	Applies to: all elements, ::before and ::after pseudo-elements
	Inherited: none
	Animatable: no
	Percentages: N/A
	Media: visual
	Computed value: As specified
	Canonical order: per grammar
	</pre>

	<dfn>&lt;single-animation-name></dfn> = none | <<IDENT>>

<h3 id="animation-duration">
The 'animation-duration' property</h3>

	The ‘animation-duration’ property defines the length of time that an animation takes to 
	complete one cycle. 

	<pre class='propdef'>
	Name: animation-duration
	Value: <<time>> [, <<time>>]*
	Initial: 0s
	Applies to: all elements, ::before and ::after pseudo-elements
	Inherited: no
	Animatable: no
	Percentages: N/A
	Media: visual
	Computed value: As specified
	Canonical order: per grammar
	</pre>

	The initial value is 0s, meaning that the animation takes no time. When the duration is 0s 
	'animation-fill-mode' still applies, so an animation that fills backwards will show the value of 
	the 0% keyframe during any delay period, and an animation that fills forwards will retain the 
	value specified at the 100% keyframe, even if the animation was instantaneous. Also, animation 
	events are still fired. A negative 'animation-duration' value renders the declaration invalid. 

<h3 id="animation-timing-function">
The 'animation-timing-function' property</h3>

	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. 

	<pre class='propdef'>
	Name: animation-timing-function
	Value: <<single-timing-function>> [ ‘,’ <<single-timing-function>> ]* 
	Initial: ease
	Applies to: all elements, ::before and ::after pseudo-elements
	Inherited: no
	Animatable: no
	Percentages: N/A
	Media: visual
	Computed value: As specified
	Canonical order: per grammar
	</pre>

	All the valid values of <dfn>&lt;single-timing-function></dfn> are defined by the 'transition-timing-function' 
	property [[!CSS3-TRANSITIONS]].

	For a keyframed animation, the 'animation-timing-function' applies between keyframes, not over the 
	entire animation. For example, in the case of an ease-in-out timing function, an animation will 
	ease in at the start of the keyframe and ease out at the end of the keyframe. An 'animation-timing-function' 
	defined within a keyframe block applies to that keyframe, otherwise the timing function specified for 
	the animation is used. In addition, only the first value of the property applies when it is used in 
	a keyframe block. 

<h3 id="animation-iteration-count">
The 'animation-iteration-count' property</h3>

	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. A value of ''infinite'' will cause the animation to repeat forever. Non-integer numbers 
	will cause the animation to end part-way through a cycle. Negative values of 
	'animation-iteration-count' are invalid. This property is often used in conjunction an 
	'animation-direction' value of ‘alternate’, which will cause the animation to play in 
	reverse on alternate cycles. 

	<pre class='propdef'>
	Name: animation-iteration-count
	Value: <<single-animation-iteration-count>> [ ‘,’ <<single-animation-iteration-count>> ]* 
	Initial: 1
	Applies to: all elements, ::before and ::after pseudo-elements
	Inherited: no
	Animatable: no
	Percentages: N/A
	Media: visual
	Computed value: As specified
	Canonical order: per grammar
	</pre>

	<dfn>&lt;single-animation-iteration-count></dfn> = infinite | <<number>>

<h3 id="animation-direction">
The 'animation-direction' property</h3>

	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. 

	<pre class='propdef'>
	Name: animation-direction
	Value: <<single-animation-direction>> [ ‘,’ <<single-animation-direction>> ]* 
	Initial: normal
	Applies to: all elements, ::before and ::after pseudo-elements
	Inherited: no
	Animatable: no
	Percentages: N/A
	Media: visual
	Computed value: As specified
	Canonical order: per grammar
	</pre>

	<dfn>&lt;single-animation-direction></dfn> = normal | reverse | alternate | alternate-reverse

	<dl dfn-type=value dfn-for=animation-direction>
		<dt><dfn>normal</dfn>
		<dd>
			All iterations of the animation are played as specified.

		<dt><dfn>reverse</dfn>
		<dd>
			All iterations of the animation are played in the reverse direction 
			from the way they were specified. 

		<dt><dfn>alternate</dfn>
		<dd>
			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. 

		<dt><dfn>alternate-reverse</dfn>
		<dd>
			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. 
	</dl>

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


<h3 id="animation-play-state">
The 'animation-play-state' property</h3>

	The 'animation-play-state' property defines whether the animation is running or paused. 
	A running animation can be paused by setting this property to ''paused''. To continue 
	running a paused animation this property can be set to ''running''. A paused animation will 
	continue to display the current value of the animation in a static state, as if the time 
	of the animation is constant. When a paused animation is resumed, it restarts from the 
	current value, not necessarily from the beginning of the animation. 

	<pre class='propdef'>
	Name: animation-play-state
	Value: <<single-animation-play-state>> [ , <<single-animation-play-state>> ]*  
	Initial: running
	Applies to: all elements, ::before and ::after pseudo-elements
	Inherited: no
	Animatable: no
	Percentages: N/A
	Media: visual
	Computed value: As specified
	Canonical order: per grammar
	</pre>

	<dfn>&lt;single-animation-play-state></dfn> = running | paused

<h3 id="animation-delay">
The 'animation-delay' property</h3>

	The 'animation-delay' property defines when the animation will start. It allows an animation 
	to begin execution some time after it is applied. An 'animation-delay' value of ‘0s’ means 
	the animation will execute as soon as it is applied. Otherwise, the value specifies an offset 
	from the moment the animation is applied, and the animation will delay execution by that offset.

	If the value for 'animation-delay' is a negative time offset then the animation will execute the 
	moment it is applied, but will appear to have begun execution at the specified offset. That is, 
	the animation will appear to begin part-way through its play cycle. In the case where an animation 
	has implied starting values and a negative 'animation-delay', the starting values are taken from 
	the moment the animation is applied. 

	<pre class='propdef'>
	Name: animation-delay
	Value: <<time>> [ , <<time>>]* 
	Initial: 0s
	Applies to: all elements, ::before and ::after pseudo-elements
	Inherited: no
	Animatable: no
	Percentages: N/A
	Media: visual
	Computed value: As specified
	Canonical order: per grammar
	</pre>

<h3 id="animation-fill-mode">
The 'animation-fill-mode' property</h3>

	 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' property). The 'animation-fill-mode' 
	 property can override this behavior.

	If the value for 'animation-fill-mode' is ''backwards'', then the animation will apply 
	the property values defined in the keyframe that will start the first iteration of the 
	animation, during the period defined by 'animation-delay'. 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'').

	If the value for 'animation-fill-mode' is ''forwards'', then 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'').

	If the value for 'animation-fill-mode' is ''both'', then the animation will follow the rules 
	for both ''forwards'' and ''backwards''. That is, it will extend the animation in both directions.  

	<pre class='propdef'>
	Name: animation-fill-mode
	Value: <<single-animation-fill-mode>> [ , <<single-animation-fill-mode>> ]*  
	Initial: none
	Applies to: all elements, ::before and ::after pseudo-elements
	Inherited: no
	Animatable: no
	Percentages: N/A
	Media: visual
	Computed value: As specified
	Canonical order: per grammar
	</pre>

	<dfn>&lt;single-animation-fill-mode></dfn> = none | forwards | backwards | both

<h3 id="animation">
The 'animation' shorthand property</h3>

	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.) 


	<pre class='propdef'>
	Name: animation
	Value: 	<<single-animation>> [ , <<single-animation>> ]*   
	Initial: see individual properties
	Applies to: all elements, ::before and ::after pseudo-elements
	Inherited: no
	Animatable: no
	Percentages: N/A
	Media: visual
	Computed value: As specified
	Canonical order: per grammar
	</pre>

	<dfn>&lt;single-animation></dfn> = <<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' 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. 

<h2 id="events">
Animation Events</h2>

	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 both a valid keyframe rule and a non-zero duration are 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. 

<h3 id="interface-animationevent">
The <code>AnimationEvent</code> Interface</h3>

	The <dfn>AnimationEvent</dfn> interface provides specific contextual information associated with 
	Animation events. 

<h4 id="interface-animationevent-idl">
IDL Definition</h4>

	<pre class="idl">
		[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 = "";
		};
	</pre>

<h4 id="interface-animationevent-attributes">
Attributes</h4>

	<dl dfn-type=attribute dfn-for=animationevent>
		<dt><dfn>animationName</dfn>, of type <a interface>DOMString</a>, readonly
		<dd>
			The value of the 'animation-name' property of the animation that fired the event. 
		<dt><dfn>elapsedTime</dfn>, of type <a interface>float</a>, readonly
		<dd>
			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).  
		<dt><dfn>pseudoElement</dfn>, of type <a interface>DOMString</a>, readonly
		<dd>
			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). 
	</dl>
	
	<dfn>AnimationEvent(type, animationEventInitDict)</dfn> is an <a href="http://dvcs.w3.org/hg/domcore/raw-file/tip/Overview.html#constructing-events">event constructor</a>.

<h3 id="event-animationevent">
Types of <code>AnimationEvent</code></h3>

	The different types of animation events that can occur are: 

	<dl dfn-type=enum>
		<dt><dfn>animationstart</dfn>
		<dd>
			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. 
			<ul>
				<li>Bubbles: Yes</li>
				<li>Cancelable: No</li>
				<li>Context Info: animationName, pseudoElement</li>
			</ul>

		<dt><dfn>animationend</dfn>
		<dd>
			The ''animationend'' event occurs when the animation finishes. 
			<ul>
				<li>Bubbles: Yes</li>
				<li>Cancelable: No</li>
				<li>Context Info: animationName, elapsedTime, pseudoElement</li>
			</ul>

		<dt><dfn>animationiteration</dfn>
		<dd>
			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.  
			<ul>
				<li>Bubbles: Yes</li>
				<li>Cancelable: No</li>
				<li>Context Info: animationName, elapsedTime, pseudoElement</li>
			</ul>
	</dl>