Explicitly disallow commas in toggle's <value>, just to make it clearer.

Author: tabatkins

css3-values/Overview.html

@@ -1574,11 +1574,12 @@ <h3 id=toggle-notation><span class=secno>8.2. </span> Toggling Between
   <pre>toggle( &lt;value># )</pre>
 
   <p> where <var>&lt;value></var> is any CSS value that is valid where the
-   expression is placed. If any of the values inside are not valid, then the
-   entire ‘<a href="#toggle"><code class=css>toggle()</code></a>’
-   expression is invalid. The ‘<a href="#toggle"><code
-   class=css>toggle()</code></a>’ expression may be used as the value of
-   any property (but must be the only component in that property's value).
+   expression is placed, and which doesn't contain any top-level commas. If
+   any of the values inside are not valid, then the entire ‘<a
+   href="#toggle"><code class=css>toggle()</code></a>’ expression is
+   invalid. The ‘<a href="#toggle"><code class=css>toggle()</code></a>’
+   expression may be used as the value of any property (but must be the only
+   component in that property's value).
 
   <p class=note> Note that because toggled values are separated by commas,
    they cannot themselves include top-level commas.

css3-values/Overview.src.html

@@ -1113,7 +1113,8 @@ <h3 id="toggle-notation">
 
 	<p>
 		where <var>&lt;value></var> is any CSS value 
-		that is valid where the expression is placed.  
+		that is valid where the expression is placed,
+		and which doesn't contain any top-level commas.  
 		If any of the values inside are not valid, 
 		then the entire ''toggle()'' expression is invalid.
 		The ''toggle()'' expression may be used as the value of any property