[css-variables] Tweak custom property grammar.

Author: tabatkins

css-variables/Overview.html

@@ -261,9 +261,9 @@ <h2 id=defining-variables><span class=secno>2. </span> Defining Custom
     <tr>
      <th>Values:
 
-     <td><a href="#ltvalue"><var>&lt;value></var></a> | <a
+     <td>[ <a href="#ltvalue"><var>&lt;value></var></a> | <a
       href="#ltcdo"><var>&lt;CDO></var></a> | <a
-      href="#ltcdc"><var>&lt;CDC></var></a>
+      href="#ltcdc"><var>&lt;CDC></var></a> ]*
 
     <tr>
      <th>Initial:
@@ -1125,7 +1125,7 @@ <h2 class=no-num id=property-index>Property index</h2>
     <tr>
      <th><a class=property href="#var-">var-*</a>
 
-     <td>&lt;value> | &lt;CDO> | &lt;CDC>
+     <td>[ &lt;value> | &lt;CDO> | &lt;CDC> ]*
 
      <td>(nothing, see prose)
 

css-variables/Overview.src.html

@@ -124,7 +124,7 @@ <h2 id="defining-variables">
 			<td><dfn>var-*</dfn>
 		<tr>
 			<th>Values:
-			<td><var>&lt;value></var> | <var>&lt;CDO></var> | <var>&lt;CDC></var>
+			<td>[ <var>&lt;value></var> | <var>&lt;CDO></var> | <var>&lt;CDC></var> ]*
 		<tr>
 			<th>Initial:
 			<td>(nothing, see prose)