[css-animations] Clarify rules on animation shorthand parsing, as discussed in the face-to-face meeting earlier today.

Author: dbaron

css-animations/Overview.bs

@@ -677,7 +677,9 @@ The 'animation' shorthand property</h3>
 
 	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
+	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.

css-animations/Overview.html

@@ -721,7 +721,9 @@ <h3 class="heading settled heading" data-level=4.10 id=animation><span class=sec
 
 <p>Note that order is also important within each animation definition for distinguishing
 	<a class="production css-code" data-link-type=type href=#typedef-single-animation-name title="<single-animation-name>">&lt;single-animation-name&gt;</a> values from other keywords. When parsing, keywords that are valid for
-	properties other than <a class=property data-link-type=propdesc href=#propdef-animation-name title=animation-name>animation-name</a> must be accepted for those properties rather than for
+	properties other than <a class=property data-link-type=propdesc href=#propdef-animation-name title=animation-name>animation-name</a>
+	whose values were not found earlier in the shorthand
+	must be accepted for those properties rather than for
 	<a class=property data-link-type=propdesc href=#propdef-animation-name title=animation-name>animation-name</a>. Furthermore, when serializing, default values of other properties must be
 	output in at least the cases necessary to distinguish an <a class=property data-link-type=propdesc href=#propdef-animation-name title=animation-name>animation-name</a> that could
 	be a value of another property, and may be output in additional cases.</p>