[css-cascade-5][editorial] Define import condition as syntax production

css-cascade-5/Overview.bs

@@ -135,11 +135,13 @@ Importing Style Sheets: the ''@import'' rule</h2>
 	or else the ''@import'' rule is invalid.
 	The syntax of ''@import'' is:
 
-	<pre class='prod'>
+<pre class='prod'>
 		@import [ <<url>> | <<string>> ]
 		        [ layer | layer(<<layer-name>>) ]?
-		        [ supports( [ <<supports-condition>> | <<declaration>> ] ) ]?
-		        <<media-query-list>>? ;</pre>
+		        <<import-condition>> ;
+
+		<dfn export>&lt;import-condition></dfn> = [ supports( [ <<supports-condition>> | <<declaration>> ] ) ]?
+		                     <<media-query-list>>? ;</pre>
 
 	where:
 
@@ -157,9 +159,8 @@ Importing Style Sheets: the ''@import'' rule</h2>
 		(just as if declared by an ''@layer'' rule wrapped
 		in the appropriate [=conditional group rules=]).
 
-	* the optional [<<supports-condition>>|<<declaration>>] and <<media-query-list>>
-		(collectively, the <dfn export>import conditions</dfn>)
-		state the conditions under which it applies.
+	* the optional <<import-condition>>
+		states the conditions under which it applies.
 
 	<div class="example">
 		The following <a href="#conditional-import">conditional <css>@import</css> rule</a>