[css-text-3][css-text-4] Compute match-parent to start on the root for implementation simplicity. w3c#6542

Author: fantasai

css-text-3/Overview.bs

@@ -4901,11 +4901,17 @@ Text Alignment: the 'text-align' shorthand</h3>
 			except that an [=inherited value=] of
 			''text-align/start'' or ''text-align/end''
 			is interpreted against the parent’s
-			(or the [=initial containing block=]’s,
-			if there is no parent)
 			'direction' value
 			and results in a computed value of either
 			''text-align/left'' or ''text-align/right''.
+			Computes to ''text-align/start''
+			when specified on the [=root element=].
+			<!-- ideally it would compute against the root writing mode
+			     and inherit as `left` or `right` for consistency in descendants,
+			     but since this is complicated due to propagation
+			     and match-parent has basically no real use case on root,
+			     we're doing this instead because it's easy -->
+
 			When specified on the 'text-align' shorthand,
 			sets both 'text-align-all' and 'text-align-last' to ''text-align/match-parent''.
 
@@ -7909,6 +7915,9 @@ Recent Changes</h3>
 			and should apply any appropriate spelling changes
 			just as for automatic hyphenation at the same point.</ins>
 		</blockquote>
+	* Define ''text-align/match-parent'' on the [=root element=] to compute to ''text-align/start''
+		instead of computing against the [=principal writing mode=].
+		(<a href="https://github.com/w3c/csswg-drafts/issues/6542">Issue 6542</a>)
 
 	In addition there have been some minor editorial fixes.
 

css-text-4/Overview.bs

@@ -6380,11 +6380,17 @@ Text Alignment: the 'text-align' shorthand</h3>
 			except that an [=inherited value=] of
 			''text-align/start'' or ''text-align/end''
 			is interpreted against the parent’s
-			(or the [=initial containing block=]’s,
-			if there is no parent)
 			'direction' value
 			and results in a computed value of either
 			''text-align/left'' or ''text-align/right''.
+			Computes to ''text-align/start''
+			when specified on the [=root element=].
+			<!-- ideally it would compute against the root writing mode
+			     and inherit as `left` or `right` for consistency in descendants,
+			     but since this is complicated due to propagation
+			     and match-parent has basically no real use case on root,
+			     we're doing this instead because it's easy -->
+
 			When specified on the 'text-align' shorthand,
 			sets both 'text-align-all' and 'text-align-last' to ''text-align/match-parent''.