[css-align] Use physical left/right as well as line-relative left/right for mapping left/right keywords. #1403

Author: fantasai

css-align/Overview.bs

@@ -303,13 +303,19 @@ Positional Alignment: the ''center'', ''start'', ''end'', ''self-start'', ''self
 			this value behaves as ''end'' when used in the <a>content-distribution properties</a>.
 
 		<dt><dfn for="<self-position>, <content-position>">left</dfn> <small>([[#self-alignment|self]], [[#content-distribution|content]])</small>
-		<dd>Aligns the <a>alignment subject</a> to be flush with the <a>alignment container</a>’s <a href="https://www.w3.org/TR/css3-writing-modes/#line-left">line-left</a> edge.
-			If the property's axis is not parallel with the inline axis,
+		<dd>Aligns the <a>alignment subject</a> to be flush with
+			the <a>alignment container</a>’s <a href="https://www.w3.org/TR/css3-writing-modes/#line-left">line-left</a>
+			or <a>phyisical left</a> edge,
+			whichever is in the appropriate axis.
+			If the property's axis is not parallel with either left↔right axis,
 			this value behaves as ''start''.
 
 		<dt><dfn for="<self-position>, <content-position>">right</dfn> <small>([[#self-alignment|self]], [[#content-distribution|content]])</small>
-		<dd>Aligns the <a>alignment subject</a> to be flush with the <a>alignment container</a>’s <a href="https://www.w3.org/TR/css3-writing-modes/#line-right">line-right</a> edge.
-			If the property's axis is not parallel with the inline axis,
+		<dd>Aligns the <a>alignment subject</a> to be flush with
+			the <a>alignment container</a>’s <a href="https://www.w3.org/TR/css3-writing-modes/#line-right">line-right</a>
+			or <a>phyisical right</a> edge,
+			whichever is in the appropriate axis.
+			If the property's axis is not parallel with either left↔right axis,
 			this value behaves as ''start''.
 	</dl>