[css-break-4] Don't extend boxes into table/grid gaps #12801

Author: fantasai

css-break-4/Overview.bs

@@ -1083,6 +1083,11 @@ Splitting Boxes</h3>
 			Illustration of filling the <a>remaining fragmentainer extent</a>.
 	</div>
 
+	However, if the fragmented box is
+	a [=grid item=] or [=table cell=] that spans multiple rows,
+	and the [=fragmentation break=] splits its container between two of those rows,
+	then the box should not extend into (or beyond) the gap between those rows.
+
 <h3 id="break-decoration">
 Fragmented Borders and Backgrounds: the 'box-decoration-break' property</h3>