[web-animations-1] Make composite member of Keyframe dictionaries accept null values.

This closes w3c#2074.

Author: birtles

web-animations-1/Overview.bs

@@ -4622,7 +4622,7 @@ interface KeyframeEffect : KeyframeEffectReadOnly {
           double?             offset = null;
           double              computedOffset;
           DOMString           easing = "linear";
-          CompositeOperation? composite;
+          CompositeOperation? composite = null;
       };
       </pre>
 
@@ -4651,8 +4651,8 @@ interface KeyframeEffect : KeyframeEffectReadOnly {
       ::  The <a>keyframe-specific composite operation</a> used to combine the
           values specified in this keyframe with the <a>underlying value</a>.
 
-          This member will be absent if the <a>composite operation</a>
-          specified on the <a>keyframe effect</a> is being used.
+          This member will be <code>null</code> if the <a>composite
+          operation</a> specified on the <a>keyframe effect</a> is being used.
 
     </div>
 
@@ -4672,10 +4672,10 @@ interface KeyframeEffect : KeyframeEffectReadOnly {
 
             <pre class='idl'>
              dictionary BaseComputedKeyframe {
-                 double?            offset = null;
-                 double             computedOffset;
-                 DOMString          easing = "linear";
-                 CompositeOperation composite;
+                 double?             offset = null;
+                 double              computedOffset;
+                 DOMString           easing = "linear";
+                 CompositeOperation? composite = null;
             };
             </pre>
 
@@ -4953,17 +4953,17 @@ WebIDL-like definition:
 dictionary Keyframe {
     // ... property-value pairs ...
     // i.e. DOMString propertyName
-    double?             offset = null;
-    DOMString           easing = "linear";
-    CompositeOperation  composite;
+    double?              offset = null;
+    DOMString            easing = "linear";
+    CompositeOperation?  composite = null;
 };
 
 dictionary PropertyIndexedKeyframes {
     // ... property-value and property-valuelist pairs ...
     // i.e. (DOMString or sequence&amp;lt;DOMString&amp;gt;) propertyName
-    (double? or sequence&lt;double?&gt;)                       offset = [];
-    (DOMString or sequence&lt;DOMString&gt;)                   easing = [];
-    (CompositeOperation or sequence&lt;CompositeOperation&gt;) composite = [];
+    (double? or sequence&lt;double?&gt;)                         offset = [];
+    (DOMString or sequence&lt;DOMString&gt;)                     easing = [];
+    (CompositeOperation? or sequence&lt;CompositeOperation?&gt;) composite = [];
 };
 
 typedef (sequence&lt;Keyframe&gt; or PropertyIndexedKeyframes) KeyframeArgument;
@@ -4996,8 +4996,8 @@ The meaning and allowed values of each argument is as follows:
 ::  The <a>keyframe-specific composite operation</a> used to combine the values
     specified in this keyframe with the <a>underlying value</a>.
 
-    If absent, the <a>composite operation</a> specified on the <a>keyframe
-    effect</a> will be used.
+    If <code>null</code>, the <a>composite operation</a> specified on the
+    <a>keyframe effect</a> will be used.
 
 
 Since this type cannot be expressed in WebIDL, its processing is defined in
@@ -5048,9 +5048,9 @@ otherwise, using the following procedure:
 
         <pre class='idl'>
         dictionary BasePropertyIndexedKeyframe {
-            (double? or sequence&lt;double?&gt;)                       offset = [];
-            (DOMString or sequence&lt;DOMString&gt;)                   easing = [];
-            (CompositeOperation or sequence&lt;CompositeOperation&gt;) composite = [];
+            (double? or sequence&lt;double?&gt;)                         offset = [];
+            (DOMString or sequence&lt;DOMString&gt;)                     easing = [];
+            (CompositeOperation? or sequence&lt;CompositeOperation?&gt;) composite = [];
         };
         </pre>
 
@@ -5059,9 +5059,9 @@ otherwise, using the following procedure:
 
         <pre class='idl'>
         dictionary BaseKeyframe {
-            double?            offset = null;
-            DOMString          easing = "linear";
-            CompositeOperation composite;
+            double?             offset = null;
+            DOMString           easing = "linear";
+            CompositeOperation? composite = null;
         };
         </pre>
 
@@ -5284,20 +5284,22 @@ keyframes using the following procedure:
         1.  If the &ldquo;composite&rdquo; member of the <var>property-indexed
             keyframe</var> is <em>not</em> an empty sequence:
 
-            1.  Let <var>composite modes</var> be a sequence of <a>composite
-                operations</a> assigned from the &ldquo;composite&rdquo; member
-                of <var>property-indexed keyframe</var>.
-                If that member is a single <a>composite operation</a>, let
-                <var>composite modes</var> be a sequence of length one, with
-                the value of the &ldquo;composite&rdquo; as its single item.
+            1.  Let <var>composite modes</var> be a sequence of <a>nullable</a>
+                <a>composite operations</a> assigned from the
+                &ldquo;composite&rdquo; member of <var>property-indexed
+                keyframe</var>.
+                If that member is a single <a>nullable</a> <a>composite
+                operation</a>, let <var>composite modes</var> be a sequence of
+                length one, with the value of the &ldquo;composite&rdquo; as its
+                single item.
 
             1.  As with <var>easings</var>, if <var>composite modes</var>
                 has fewer items than <var>processed keyframes</var>, repeat the
                 elements in <var>composite modes</var> successively starting
                 from the beginning of the list until <var>composite modes</var>
                 has as many items as <var>processed keyframes</var>.
 
-            1.  Assign each value in <var>composite modes</var> to the
+            1.  Assign each non-null value in <var>composite modes</var> to the
                 <a>keyframe-specific composite operation</a> on the
                 <a>keyframe</a> with the corresponding position in
                 <var>processed keyframes</var> until the end of <var>processed
@@ -5901,8 +5903,9 @@ The following changes have been made since the <a
     programming interface using <code>cssOffset</code> to avoid conflict with
     the attribute name used to specify keyframe offsets.
 *   Updated the procedure to <a>process a keyframes argument</a> to allow
-    specifying <code>offset</code>, <code>composite</code> and mulitple
-    <code>easing</code> values.
+    specifying <code>offset</code>, <code>composite</code> and multiple
+    <code>easing</code> values including allowing <code>null</code> values for
+    <code>composite</code>.
 *   Changed the type of the
     {{KeyframeEffectReadOnly/KeyframeEffectReadOnly(target, keyframes,
     options)/target}} argument to the {{KeyframeEffect}} and