[css-contain-3] Disallow not/none for container-name in @-rule. w3c#7203

Use a separate definition of container-name in the @container syntax to
disallow 'none' and 'not'.

Author: lilles

css-contain-3/Overview.bs

@@ -577,6 +577,7 @@ Container Queries: the ''@container'' rule</h3>
 	where:
 
 	<pre class="prod def">
+	<dfn id="query-container-name"><<container-name>></dfn> = <<custom-ident>>
 	<dfn><<container-condition>></dfn> = not <<query-in-parens>>
 	                      | <<query-in-parens>> [ [ and <<query-in-parens>> ]* | [ or <<query-in-parens>> ]* ]
 	<dfn><<query-in-parens>></dfn>     = ( <<container-condition>> )
@@ -592,14 +593,15 @@ Container Queries: the ''@container'' rule</h3>
 	                      | <<general-enclosed>>
 	</pre>
 
+	The keywords ''container-name/none'' and ''not'' are excluded from the <<custom-ident>> above.
 
 	For each element,
 	the [=query container=] to be queried
 	is selected from among the element’s ancestor [=query containers=]
 	that have a valid 'container-type'
 	for all the [=container features=]
 	in the <<container-condition>>.
-	The optional <dfn><<container-name>></dfn>
+	The optional <<container-name>>
 	filters the set of [=query containers=] considered
 	to just those with a matching [=query container name=].