[css-align] Deal with 'stretch' and 'last baseline' case. w3c#1556

Author: fantasai

css-align/Overview.bs

@@ -987,7 +987,12 @@ Inline/Main-Axis Alignment: the 'justify-self' property</h3>
 			sets the box’s used size to the length necessary to make its outer size
 			as close to filling the <a>alignment container</a> as possible
 			while still respecting the constraints imposed by 'min-height'/'min-width'/'max-height'/'max-width'.
-			Unless otherwise specified, this value falls back to ''flex-start''.
+
+			Unless otherwise specified, this value falls back to ''flex-start'' generally,
+			and to ''self-start'' or ''self-end''
+			if the box has also specified
+			<a>first baseline</a> or <a>last baseline</a> <a>baseline content-alignment</a> (respectively)
+			in the same axis.
 
 			Note: The ''justify-self/stretch'' keyword can cause elements to shrink,
 			to fit their container.