[css-counter-styles] Change override to extends. Add example.

--HG--
extra : rebase_source : 3eed1663aeb0007fe4e0d73fabfe2dfa92c3d61e

Author: tabatkins

css-counter-styles/Overview.bs

@@ -658,34 +658,56 @@ Accumulating Numerals: the ''additive'' system</h4>
 	relative to the size of the counter value.
 
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-<h4 id="override-system">
-Tweaking Existing Counter Styles: the ''override'' system</h4>
+<h4 id="extends-system">
+Tweaking Existing Counter Styles: the ''extends'' system
+<span id='override-system'></span></h4>
 
-	The <dfn value for="@counter-style/system">override</dfn> system allows an author to use the algorithm of another counter style,
+	The <dfn value for="@counter-style/system">extends</dfn> system allows an author to use the algorithm of another counter style,
 	but alter other aspects,
 	such as the negative sign or the suffix.
-	If a counter style uses the ''override'' system,
-	any unspecified descriptors must be taken from the overridden counter style specified,
+	If a counter style uses the ''extends'' system,
+	any unspecified descriptors must be taken from the extended counter style specified,
 	rather than taking their initial values.
 
-	If a @counter-style uses the ''override'' system,
+	If a @counter-style uses the ''extends'' system,
 	it must not contain a 'symbols' or 'additive-symbols' descriptor,
 	or else the ''@counter-style'' rule is invalid.
 
 	If the specified counter style name isn't the name of any currently-defined counter style,
-	it must be treated as if it was overriding the ''decimal'' counter style.
-	If one or more ''@counter-style'' rules form a cycle with their ''override'' values,
+	it must be treated as if it was extending the ''decimal'' counter style.
+	If one or more ''@counter-style'' rules form a cycle with their ''extends'' values,
 	all of the counter styles participating in the cycle
-	must be treated as if they were overriding the ''decimal'' counter style instead.
+	must be treated as if they were extending the ''decimal'' counter style instead.
+
+	<div class='example'>
+		For example, if you wanted a counter style that was identical to decimal,
+		but used a parenthesis rather than a period after it, like:
+
+		<pre>
+		1) first item
+		2) second item
+		3) third item
+		</pre>
+
+		Rather than writing up an entirely new counter style,
+		this can be done by just extending ''decimal'':
+
+		<pre class='css'>
+		@counter-style decimal-paren {
+			system: extends decimal;
+			suffix: ") ";
+		}
+		</pre>
+	</div>
 
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@@ -2341,6 +2363,8 @@ Changes since the July 2013 Working Draft</h2>
 		<li>Fix ''ethiopic-numeric'' algorithm step 5.
 
 		<li>Extended Korean styles to handle negative numbers.
+
+		<li>Changed "override" system to ''extends''.
 	</ul>
 
 	A <a href="http://dev.w3.org/csswg/css-counter-styles-3/issues-lc-20130718">Disposition of Comments</a> is available.