[css-animations-1] Define indexed property getter for CSSKeyframesRule

Author: birtles

css-animations-1/Overview.bs

@@ -1117,7 +1117,9 @@ IDL Definition</h4>
 	interface CSSKeyframesRule : CSSRule {
 	           attribute CSSOMString name;
 	  readonly attribute CSSRuleList cssRules;
+	  readonly attribute unsigned long length;
 
+	  getter CSSKeyframeRule (unsigned long index);
 	  undefined        appendRule(CSSOMString rule);
 	  undefined        deleteRule(CSSOMString select);
 	  CSSKeyframeRule? findRule(CSSOMString select);
@@ -1136,8 +1138,39 @@ Attributes</h4>
 		<dt><dfn>cssRules</dfn>
 		<dd>
 			This attribute gives access to the keyframes in the list.
+
+		<dt><dfn>length</dfn>
+		<dd>
+			This attribute is the number of keyframes in the list.
+	</dl>
+
+<h4 id="interface-csskeyframesrule-indexed-property-getter">
+The indexed property getter</h4>
+
+	The <dfn method for="CSSKeyframesRule" lt="__getter__(index)">indexed property
+	getter</dfn> returns the {{CSSKeyframeRule}} from the list of keyframes
+	at the indicated position.
+
+	Parameters:
+
+	<dl>
+
+		<dt><dfn argument for="CSSKeyframesRule/__getter__(index)">index</dfn>
+		of type {{unsigned long}}
+		<dd>
+			The zero-based index of the rule to return.
+	</dl>
+
+	Return Value:
+
+	<dl>
+		<dt>{{CSSKeyframeRule}}
+		<dd>
+			The found rule or {{undefined}} if there is no rule at the specific index.
 	</dl>
 
+	No Exceptions
+
 <h4 id="interface-csskeyframesrule-appendrule">
 The <code>appendRule</code> method</h4>