[css-overflow-3] Add issue about transforms and overflow.

Author: tabatkins

css-overflow-3/Overview.bs

@@ -233,6 +233,16 @@ Scrollable overflow</h3>
 	in the box's own coordinate system, but might be non-rectangular
 	in other coordinate systems due to transforms [[CSS3-TRANSFORMS]].
 
+	Issue: Browsers seem to agree on using axis-aligned rectangles (in the element's own coord space)
+	to determine overflow.
+	This means scrollbars can appear when not actually necessary.
+	See <a href="http://software.hixie.ch/utilities/js/live-dom-viewer/?%3C!DOCTYPE%20html%3E%0A%3Cdiv%20class%3Dparent%3E%3Cdiv%20class%3Dchild%3E%3Cdiv%20class%3D%27grandchild%27%3E%3C%2Fdiv%3E%3C%2Fdiv%3E%3C%2Fdiv%3E%0A%3Cstyle%3E%0Adiv%20{%20padding%3A%2030px%3B%20min-width%3A%2030px%3B%20float%3A%20left%3B%20border%3A%20thin%20dotted%3B%20background%3A%20rgba%280%2C0%2C0%2C.2%29%3B}%0A.parent%20{%20overflow%3A%20auto%3B%20background%3A%20rgba%28255%2C0%2C0%2C.2%29%3B%20}%0A.child%20{%20transform%3A%20rotate%28-45deg%29%3B%20padding%3A%203px%3B%20background%3A%20rgba%280%2C255%2C0%2C.2%29%3B%20}%0A.grandchild%20{%20transform%3A%20rotate%2845deg%29%20scale%28.9%29%3B%20background%3A%20rgba%280%2C0%2C255%2C.2%29%3B%20}">testcase</a>
+	(adjust the ''scale(.9)'' to ''scale(.7)'' to see the scrollbars disappear,
+	as the blue grandchild is no longer growing the bounds of the green child).
+	Is this behavior we want to spec,
+	or is it something browsers would like to fix someday?
+
+
 <h3 id="border-box">
 Border box overflow</h3>