[css-counter-styles] Handle override cycles.

Author: tabatkins

css-counter-styles/Overview.bs

@@ -584,8 +584,12 @@ Tweaking Existing Counter Styles: the ''override'' system</h4>
 	If a @counter-style uses the ''override'' 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,
+	all of the counter styles participating in the cycle
+	must be treated as if they were overriding the ''decimal'' counter style instead.
 
 
 <h3 id='counter-style-negative'>

css-counter-styles/Overview.html

@@ -707,8 +707,12 @@ <h4 class="heading settled heading" data-level=3.1.7 id=override-system><span cl
 <p>	If a @counter-style uses the <a class=css data-link-type=maybe href=#valuedef-override title=override>override</a> system,
 	it must not contain a <a class=property data-link-type=propdesc href=#descdef-symbols title=symbols>symbols</a> or <a class=property data-link-type=propdesc href=#descdef-additive-symbols title=additive-symbols>additive-symbols</a> descriptor,
 	or else the <a class=css data-link-type=maybe href=#at-ruledef-counter-style title=@counter-style>@counter-style</a> rule is invalid.
-	If the specified counter style name isn’t the name of any currently-defined counter style,
+
+<p>	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 <a class=css data-link-type=maybe href=#valuedef-decimal title=decimal>decimal</a> counter style.
+	If one or more <a class=css data-link-type=maybe href=#at-ruledef-counter-style title=@counter-style>@counter-style</a> rules form a cycle with their <a class=css data-link-type=maybe href=#valuedef-override title=override>override</a> values,
+	all of the counter styles participating in the cycle
+	must be treated as if they were overriding the <a class=css data-link-type=maybe href=#valuedef-decimal title=decimal>decimal</a> counter style instead.
 
 
 <h3 class="heading settled heading" data-level=3.2 id=counter-style-negative><span class=secno>3.2 </span><span class=content>