[css-syntax-3][editorial] Export declaration for use in css-conditional-5

Author: kbabbitt

css-syntax-3/Overview.bs

@@ -1975,7 +1975,7 @@ CSS Parsing Results</h3>
 			where the prelude is a selector [[selectors-4]]
 			and its declarations are [=properties=].
 
-		<dt><dfn id="declaration">declaration</dfn>
+		<dt><dfn export id="declaration">declaration</dfn>
 		<dd>
 			A declaration has a name which is a [=string=],
 			a value consisting of a list of [=component values=],