[css-cascade-5] Make anonymous layer @imports use keyword form. w3c#5681

Author: fantasai

css-cascade-5/Overview.bs

@@ -125,15 +125,23 @@ Importing Style Sheets: the ''@import'' rule</h2>
 
 	<pre class='prod'>
 		@import [ <<url>> | <<string>> ]
-						[ layer(<<layer-ident>>?) ]?
+		        [ layer | layer(<<layer-ident>>) ]?
 		        [ supports( [ <<supports-condition>> | <<declaration>> ] ) ]?
 		        <<media-query-list>>? ;</pre>
 
-	where the <<url>> or <<string>> gives the URL of the style sheet to be imported,
-	the optional <<layer-ident>> assigns imported rules to the indicated [=cascade layer=],
-	and the optional [<<supports-condition>>|<<declaration>>] and <<media-query-list>>
-	(collectively, the <dfn export>import conditions</dfn>)
-	state the conditions under which it applies.
+	where:
+
+	* the <<url>> or <<string>>
+		gives the URL of the style sheet to be imported.
+
+	* the optional ''layer'' keyword or ''layer()'' function
+		assigns the contents of the style sheet
+		into its own anonymous [=cascade layer=]
+		or into the named [=cascade layer=].
+
+	* the optional [<<supports-condition>>|<<declaration>>] and <<media-query-list>>
+		(collectively, the <dfn export>import conditions</dfn>)
+		state the conditions under which it applies.
 
 	<div class="example">
 		The following <a href="#conditional-import">conditional <css>@import</css> rule</a>