[css-cascade-5] Disallow empty @layer interspersed with @import or @namespace, #6522

Author: mirisuzanne

css-cascade-5/Overview.bs

@@ -123,7 +123,9 @@ Importing Style Sheets: the ''@import'' rule
 		as if they were written literally into the stylesheet at the point of the ''@import''.
 
 	Any ''@import'' rules must precede all other valid at-rules and style rules in a style sheet
-	(ignoring ''@charset'' and empty ''@layer'' definitions), or else the ''@import'' rule is invalid.
+	(ignoring ''@charset'' and empty ''@layer'' definitions),
+	and must not have any other valid at-rules or style rules between it and previous ''@import'' rules,
+	or else the ''@import'' rule is invalid.
 	The syntax of ''@import'' is:
 
 	
@@ -1392,7 +1394,7 @@ Anonymous Layers
 
 		* Multiple unnamed layer rules
 			place their styles into separate layers,
-			as each occurence is referencing a distinct anonymous layer name.
+			as each occurrence is referencing a distinct anonymous layer name.
 
 			
 			@layer { /* layer 1 */ }
@@ -1610,8 +1612,9 @@ Declaring Without Styles: the ''@layer'' statement at-rule
 		@layer <>#;
 	
 
-	Such empty ''@layer'' rules are allowed
-	anywhere either ''@import'' or other ''@layer'' rules are allowed.
+	Such empty ''@layer'' rules are allowed before and after ''@import'' and ''@namespace'' rules,
+	but are not allowed between (or intermixed with) ''@import'' and ''@namespace'' rules,
+	and may not precede any ''@charset'' rule.
 
 	Unlike the [[#layer-block|block syntax]],
 	multiple comma-separated layer names can be provided in this syntax,