[css-contain] Clarify effects of size containment on intrinsic aspect ratio

Closes w3c#5585

Author: frivoal

css-contain-1/Overview.bs

@@ -494,7 +494,11 @@ Size Containment</h3>
 		contain-size-replaced-005.html
 		contain-size-replaced-006.html
 		</wpt>
-	2. [=size containment/Containing boxes=] for <a>size containment</a> are <a spec=css-break-3>monolithic</a> (See [[CSS-BREAK-3#possible-breaks]]).
+
+	2. [=size containment/Containing boxes=] for <a>size containment</a> must be treated
+		as if they had no [=intrinsic aspect ratio=].
+
+	3. [=size containment/Containing boxes=] for <a>size containment</a> are <a spec=css-break-3>monolithic</a> (See [[CSS-BREAK-3#possible-breaks]]).
 
 		<wpt>
 		contain-size-breaks-001.html
@@ -906,6 +910,8 @@ This appendix is <em>informative</em>.
 				phrasing improvement in note in [[#containment-paint]]
 
 		</ul>
+	<li>
+		Be explicit that size containment suppresses intrinsic aspect ratio
 </ul>
 
 <h3 id="2019-04-30-changes">Changes from the

css-contain-2/Overview.bs

@@ -542,7 +542,11 @@ Size Containment</h3>
 		contain-size-replaced-005.html
 		contain-size-replaced-006.html
 		</wpt>
-	2. [=size containment/Containing boxes=] for <a>size containment</a> are <a spec=css-break-3>monolithic</a> (See [[CSS-BREAK-3#possible-breaks]]).
+
+	2. [=size containment/Containing boxes=] for <a>size containment</a> must be treated
+		as if they had no [=intrinsic aspect ratio=].
+
+	3. [=size containment/Containing boxes=] for <a>size containment</a> are <a spec=css-break-3>monolithic</a> (See [[CSS-BREAK-3#possible-breaks]]).
 
 		<wpt>
 		contain-size-breaks-001.html
@@ -1564,6 +1568,7 @@ Changes from <a href="https://www.w3.org/TR/2019/WD-css-contain-2-20191111/">201
 * Define the interaction between [=paint containment=] and 'overflow-clip-margin'
 * Add the 'content-visibility' property
 * Editorial improvements and clarifications to size and paint containment (in sync with the same improvements made to Level 1)
+* Be explicit that size containment suppresses intrinsic aspect ratio (in sync with the same improvements made to Level 1)
 
 <h3 id="l1-changes">
 Changes from <a href="https://www.w3.org/TR/css-contain-1/">CSS Containment Level 1</a>