[css-position-3] auto margin resolution of negative remaining space is different in vertical vs horizontal axes per CSS2. w3c#5374

Author: fantasai

css-position-3/Overview.bs

@@ -908,10 +908,13 @@ Auto Margins of Absolutely-Positioned Boxes</h3>
 	minus the box's used size in the relevant axis,
 	and this <var>remaining space</var> is divided among
 	any ''margin/auto'' margins in the relevant axis.
-	However, if the <var>remaining space</var> is negative
+	However, if
+	(all with respect to the [=writing mode=] of the [=containing block=]),
+	in the [=inline axis=]
+	the <var>remaining space</var> is negative
 	and both margins are ''margin/auto'',
-	the start margin resolves to zero
-	and the end margin receives the <var>remaining space</var>.
+	the [=inline-start|start=] margin resolves to zero
+	and the [=inline-end|end=] margin receives the <var>remaining space</var>.
 
 <h2 id="abspos-old">
 Old Absolute Positioning Layout Model</h2>