Specified that unknown descriptors don't invalidate the rule.

Author: tabatkins

css3-lists/Overview.html

@@ -1468,7 +1468,9 @@ <h2 id=counter-style><span class=secno>8. </span> Defining Custom Counter
    descriptors apply to or whether the values are inherited by child
    elements. When a given descriptor occurs multiple times in a given
    @counter-style rule, only the last specified value is used; all prior
-   values for that descriptor must be ignored.
+   values for that descriptor must be ignored. Unknown descriptors must be
+   ignored; they must not make the &lsquo;<code
+   class=css>@counter-style</code>&rsquo; rule invalid.
 
   <p>Defining a &lsquo;<code class=css>@counter-style</code>&rsquo; must make
    it available to the entire document in which it is included. If multiple

css3-lists/Overview.src.html

@@ -888,7 +888,7 @@ <h2 id='counter-style'>
 	There is no notion of which elements the descriptors apply to or whether the
 	values are inherited by child elements.  When a given descriptor occurs 
 	multiple times in a given @counter-style rule, only the last specified value
-	is used; all prior values for that descriptor must be ignored.</p>
+	is used; all prior values for that descriptor must be ignored.  Unknown descriptors must be ignored; they must not make the ''@counter-style'' rule invalid.</p>
 
 	<p>Defining a ''@counter-style'' must make it available to the entire document in which it is included.  If multiple ''@counter-style'' rules are defined with the same name, standard cascade rules must be used to determine which declaration "wins": first, they are compared by origin, with author rules beating user rules, and user rules beating UA rules; second, they are compared by document order, with later rules beating earlier rules.  ''@counter-style'' rules cascade "atomically" - if one replaces another of the same name, it replaces it <em>entirely</em>, rather than just replacing the specific descriptors it specifies.</p>