[css-grid-2] Generate separate hypoth items for each edge, so assymmetric mbp is handled correctly. #7465

Author: tabatkins

css-grid-2/Overview.bs

@@ -3861,13 +3861,11 @@ Subgrids</h2>
 			for each span size
 			in the set of items spanning into
 			the occupied track closest to that edge of the subgrid.
-			This item’s sizes are taken from the sizes of the largest such item
+			The hypothetical item’s sizes are taken from the sizes of the largest such item
 			of each span size,
 			and are additionally inflated by the subgrid’s own margin/border/padding
-			at that edge (or both edges,
-			if it happens to be the most extreme item on both sides
-			and is also the smallest span size).
-			Similarly, the hypothetical item’s span is taken
+			at that edge.
+			Correspondingly, the hypothetical item’s span is taken
 			from that same real item’s span,
 			and inflated by the number of empty tracks between it
 			and the relevant [=subgrid=]’s edge(s).
@@ -3896,14 +3894,6 @@ Subgrids</h2>
 				spanning the first two columns;
 				and one with the size of <var>a</var> plus 25px,
 				spanning the first three columns.
-
-				If only item <var>a</var> existed,
-				which would make it both
-				span into the closest occupied columns on both sides
-				and be the smallest-spanning item on each side,
-				then the hypothetical item it contributes
-				would be its size inflated by 50px
-				and would span all four columns.
 			</div>
 
 		<li id="subgrid-box-alignment">