[css-nesting-1][editorial] Add a note recommending against mixing properties and nested rules willy-nilly. #8349.

Author: tabatkins

css-nesting-1/Overview.bs

@@ -873,6 +873,15 @@ Mixing Nesting Rules and Declarations {#mixing}
 		before "Order Of Appearance" comes into consideration.
 	</div>
 
+	Note: While one <em>can</em> freely intermix declarations and nested rules,
+	it's harder to read and somewhat confusing to do so,
+	since all the properties <em>act as if</em> they came before all the rules.
+	For readability's sake,
+	it's recommended that authors put all their properties first in a style rule,
+	before any nested rules.
+	(This also happens to act slightly better in older user agents,
+	due to specifics of how parsing and error-recovery work.)
+
 
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