[css-text-decor-4] Clarify cases that are not covered by the MUST requirements for line position adjustments, to highlight where the UA has discretion.

Author: fantasai

css-text-decor-4/Overview.bs

@@ -715,7 +715,10 @@ Text Decoration Line Uniformity</h3>
 	with 'vertical-align' values other than ''vertical-align/baseline'' [[!CSS2]]
 	or subscripted/superscripted via 'font-variant-position' [[!CSS-FONTS-3]],
 	but <em>must not</em> adjust the line position or thickness
-	in response to descendants of a <i>decorating box</i> that are so styled.
+	in response to descendants of a <i>decorating box</i> that are so styled
+	(even though it <em>may</em> adjust the position
+	to accommodate descendants that are not so styled,
+	such as those merely typeset in a different font size as noted above).
 	This allows superscripts and subscripts to be properly decorated
 	(underlined, struck through, etc.)
 	but prevents them from distorting or breaking the positioning of such decorations on their ancestors.