[css-sizing-4] Define effect of aspect ratio on size constraints. #5257

Author: fantasai

css-sizing-4/Overview.bs

@@ -200,6 +200,24 @@ Intrinsic Aspect Ratios: the 'aspect-ratio' property</h3>
 	at least one of these sizes must be ''width/auto'' (/''flex-basis/content'')
 	for the <a>preferred aspect ratio</a> to have an impact on sizing.
 
+	Additionally, sizing constraints in an axis
+	(the <var>origin</var> axis)
+	are transferred through the [=preferred aspect ratio=]
+	to the other axis (the <var>destination</var> axis)
+	as follows:
+
+	* First, any [=definite=] [=minimum size=] is converted and transferred
+		from the <var>origin</var> to <var>destination</var> axis.
+		This transferred minimum is clamped
+		by any [=definite=] [=preferred size|preferred=] or [=maximum size=]
+		in the <var>destination</var> axis.
+	* Then, any [=definite=] [=maximum size=] is converted and transferred
+		from the <var>origin</var> to <var>destination</var>.
+		This transferred minimum is floored
+		by any [=definite=] [=preferred size|preferred=] or [=minimum size=]
+		in the <var>destination</var> axis
+		as well as by the transferred minimum, if any.
+
 	<div class="example">
 		This example sets each item in the grid to render as a square,
 		determining the number of items and their widths by the available space.