[css-containment] File an issue about layout containment - scrollbars mean the contents still *can* affect the layout outside of them. ;_;

Author: tabatkins

css-containment/Overview.bs

@@ -148,6 +148,12 @@ Layout Containment</h3>
 		if the containing element is off-screen or obscured,
 		the layout of its contents can be delayed or done at a lower priority.
 
+		Issue: This actually requires <a>paint containment</a> as well,
+		since an abspos or negative-margin element can protrude out
+		and cause a scrollbar to appear on a containing element,
+		thus affecting layout.
+		This isn't an issue with overlay scrollbars.
+
 	3. When laying out the page,
 		the contents of separate containing elements
 		can be laid out in parallel,