[css-text-4][editorial] Gloss out-of-flow jargon (#13030)

Author: cvrebert

css-text-4/Overview.bs

@@ -7950,7 +7950,7 @@ Hyphenation Control: the 'hyphens' property</h4>
 	For the purpose of the 'hyphens' property,
 	what constitutes a “word” is UA-dependent.
 	However, inline element boundaries
-	and out-of-flow elements
+	and [=out-of-flow=] elements
 	must be ignored when determining word boundaries.
 
 	<wpt>
@@ -13189,7 +13189,7 @@ Word and Phrase Detection</h2>
 
 		<li id=boundary-outermost>
 			Inline box boundaries
-			and out-of-flow elements must be ignored
+			and [=out-of-flow=] elements must be ignored
 			when determining word or phrase boundaries.
 			However,
 			if a [=word boundary|word=] or [=phrase boundary=] is found at the same position as