[css-text-4] Match closing-opening bracket pair trimming to JLREQ per #1668. Issue remains open for discussion around mismatched font sizes.

Author: fantasai

css-text-4/Overview.bs

@@ -1110,6 +1110,7 @@ Fullwidth Punctuation Collapsing</h4>
 			Set <a>fullwidth opening punctuation</a> half-width if the previous character is
 			a <a>fullwidth opening punctuation</a>,
 			<a>fullwidth middle dot punctuation</a>,
+			<a>fullwidth closing punctuation</a>,
 			or ideographic space (U+3000).
 			Else set it full-width.
 		<li>
@@ -1118,16 +1119,25 @@ Fullwidth Punctuation Collapsing</h4>
 			<a>fullwidth middle dot punctuation</a>,
 			or ideographic space (U+3000).
 			Else set it full-width.
-		<li>
-			Set <a>fullwidth closing punctuation</a> followed by <a>fullwidth opening punctuation</a>
-			each at "3/4-width", i.e. halfway between full-width and half-width.
 	</ul>
 
+	ISSUE: The above handling of opening&mdash;closing bracket pairs
+	matches [[JLREQ]]
+	but does not correctly handle the case of mismatched font sizes.
+	Earlier drafts trimmed 1/4 of each character, essentially averaging the spacing.
+	Other options are possible: use smallest, use largest, use common ancestor (like 'letter-spacing')...
+	See <a href="https://github.com/w3c/csswg-drafts/issues/1668#issuecomment-320212394">issue/discussion</a>.
+
 	<div class="example">
 		The following example table lists the punctuation pairs
 		affected by adjancent-pairs trimming.
 		It uses halfwidth equivalents to approximate the trimming effect.
 
+		<style>
+			.char { border: 1px dotted gray; }
+			.quarter { font-size: 25%; }
+			samp[lang="ja"] { font-family: "MS Gothic", "Osaka-Mono", monospace }
+		</style>
 		<table class="data">
 			<caption>Demonstration of adjacent-pairs punctuation trimming</caption>
 			<thead>
@@ -1143,7 +1153,7 @@ Fullwidth Punctuation Collapsing</h4>
 						<td><samp lang="ja" class="char">・</samp><samp lang="ja" class="char">(</samp>
 				<tr><th scope=row>Closing&#8212;Opening
 						<td><samp lang="ja" class="char">〕</samp>+<samp lang="ja" class="char">（</samp>
-						<td><samp lang="ja" class="char">)<span class="quarter">&#x3000;</span></samp><samp lang="ja" class="char"><span class="quarter">&#x3000;</span>(</samp>
+						<td><samp lang="ja" class="char">〕</samp><samp lang="ja" class="char">(</samp>
 				<tr><th scope=row>Ideographic Space&#8212;Opening
 						<td><samp lang="ja" class="char">　</samp>+<samp lang="ja" class="char">（</samp>
 						<td><samp lang="ja" class="char">　</samp><samp lang="ja" class="char">(</samp>