[css-flexbox-2] Tiebreak balance assignments by biasing toward earlier assignments.

Author: tabatkins

css-flexbox-2/Overview.bs

@@ -4193,6 +4193,7 @@ Balancing Flex Items</h3>
 			and it could be assigned either to the end of the preceding sequence
 			or the beginning of the next sequence,
 			it is assigned to the end of the preceding sequence.
+			Otherwise, it's assigned to the beginning of the next sequence.
 		* Calling the difference between the |line size|
 			and the [=flex container's=] [=inner size|inner=] [=main size=]
 			a sequence's |error|,
@@ -4204,14 +4205,17 @@ Balancing Flex Items</h3>
 		is its [=outer size|outer=] [=hypothetical main size=],
 		floored at 0.
 
+		If multiple possible sequence assignments
+		have equal minimum |error|,
+		select the sequence that assigns the most items to the first line;
+		if multiple sequences tie by that metric,
+		select the sequence among them that assigns the most items to the second line;
+		etc.
+
 		Assign each sequence of [=flex items=]
 		to the corresponding [=flex line=].
 	</div>
 
-	Issue: Can there be multiple equally valid sequence assignments?
-	If so, do we care which we choose?
-	Do the efficient algos make it possible to reasonably choose between them?
-
 	Note: Because all items have zero or positive size,
 	and thus adding an item to a line never increases the error,
 	there are efficient, nearly linear algorithms