[css-counter-styles] Specify that an unknown <counter-style-name> in counter()/etc acts like 'decimal'. (I think I intended to only do this in Lists, but wtv.)

--HG--
extra : rebase_source : 2f0f11687ba104a85c1e40f0fd166b376ec299b0

Author: tabatkins

css-counter-styles/Overview.bs

@@ -1037,6 +1037,9 @@ Extending 'list-style-type', ''counter()'', and ''counters()''</h2>
 		<dfn type>&lt;counter-style></dfn> = <<counter-style-name>> | <a>symbols()</a>;
 	</pre>
 
+	If a <<counter-style-name>> is used that does not refer to any existing counter style,
+	it must act identically to the ''decimal'' counter style.
+
 
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