[css-cascade] Clarify @import to not mess with relative-ordering features, and let features explicitly not work for imported sheets.

Author: tabatkins

css-cascade-3/Overview.bs

@@ -45,7 +45,17 @@ Importing Style Sheets: the ''@import'' rule</h2>
 
 	The <dfn>@import</dfn> rule allows users to import style rules from other style sheets.
 	If an ''@import'' rule refers to a valid stylesheet,
-	user agents must treat the contents of the stylesheet as if they were written in place of the ''@import'' rule.
+	user agents must treat the contents of the stylesheet as if they were written in place of the ''@import'' rule,
+	with two exceptions:
+
+	* If a feature <em>explicitly</em> defines that it only applies to a particular stylesheet,
+		and not any imported ones
+		(such as the ''@namespace'' rule),
+		then it doesn't apply to the imported stylesheet.
+	* If a feature relies on the relative position of two or more constructs in a stylesheet
+		(such as the requirement that an ''@else'' rule follow another <a>conditional group rule</a>,
+		or the requirement that ''@charset'' must not have any other content preceding it),
+		it only applies between constructs in the same stylesheet.
 
 	<p class='example'>
 		For example, declarations in style rules from imported stylesheets interact with the cascade

css-cascade/Overview.bs

@@ -58,7 +58,17 @@ Importing Style Sheets: the ''@import'' rule</h2>
 
 	The <dfn>@import</dfn> rule allows users to import style rules from other style sheets.
 	If an ''@import'' rule refers to a valid stylesheet,
-	user agents must treat the contents of the stylesheet as if they were written in place of the ''@import'' rule.
+	user agents must treat the contents of the stylesheet as if they were written in place of the ''@import'' rule,
+	with two exceptions:
+
+	* If a feature <em>explicitly</em> defines that it only applies to a particular stylesheet,
+		and not any imported ones
+		(such as the ''@namespace'' rule),
+		then it doesn't apply to the imported stylesheet.
+	* If a feature relies on the relative position of two or more constructs in a stylesheet
+		(such as the requirement that an ''@else'' rule follow another <a>conditional group rule</a>,
+		or the requirement that ''@charset'' must not have any other content preceding it),
+		it only applies between constructs in the same stylesheet.
 
 	<p class='example'>
 		For example, declarations in style rules from imported stylesheets interact with the cascade