[css-content-3] Prevent negative quote depth, matching CSS2. w3c#2038

Author: fantasai

css-content-3/Overview.bs

@@ -482,22 +482,28 @@ The *-quote values of the content property</h4>
 	Each occurrence of ''open-quote'' or ''close-quote''
 	is replaced by a quotation mark string
 	as defined by the [=quotation mark system=] specified by the 'quotes' property,
-	based on the depth of nesting.
+	based on the [=quote depth|depth of nesting=].
 
-	Which pair of quotes is used depends on the nesting level of quotes:
+	Which pair of quotes is used depends on the nesting level of quotes
+	(the <dfn>quote depth</dfn>):
 	the number of occurrences of ''open-quote'' in all generated text before the current occurrence,
 	minus the number of occurrences of ''close-quote''.
 	If the depth is 0, the first pair is used,
 	if the depth is 1, the second pair is used, etc.
 	If the depth is greater than the number of pairs,
 	the last pair is repeated.
 
-	Note: Quote depth is independent of
+	Note: [=Quote depth=] is independent of
 	the nesting of the source document or the formatting structure.
 	Also, like [[css-lists-3#inheriting-counters|counter inheritance]],
 	it operates on the “flattened element tree”
 	in the context of the [[DOM]].
 
+	A ''close-quote'' or ''no-close-quote'' that would make the [=quote depth=] negative
+	is in error and is ignored (at rendering time):
+	the depth stays at 0 and no quote mark is inserted
+	(although the rest of the 'content' property's value is still inserted).
+
 	<div class="example">
 		Some typographic styles require open quotation marks to be repeated
 		before every paragraph of a quote spanning several paragraphs,
@@ -1349,6 +1355,9 @@ bookmark-state</h3>
 			(<a href="https://github.com/w3c/csswg-drafts/issues/5478">Issue 5478</a>)
 		<li>Added ''quotes/match-parent'' value to 'quotes'.
 			(<a href="https://github.com/w3c/csswg-drafts/issues/5478">Issue 5478</a>)
+		<li>Prevent negative [=quote depth=] by ignoring excess closing quotes,
+			consistent with [[CSS2]].
+			(<a href="https://github.com/w3c/csswg-drafts/issues/2038">Issue 2034</a>)
 		<li>Miscellaneous editorial spec clean up.
 	</ul>