[css-containment][css-overflow] Remove dependency of containment on overflow:clip (w3c#829)

Author: frivoal

css-containment/Overview.bs

@@ -278,11 +278,14 @@ Paint Containment</h3>
 
 	Giving an element <dfn export>paint containment</dfn> has the following effects:
 
-	1. If the computed value of overflow-x or overflow-y would otherwise have been ''overflow/visible'',
-		it must instead compute to ''overflow/clip''. [[!CSS-OVERFLOW-3]]
-		<span class=note>This means that regardless of the specified value of 'overflow',
-		the contents of the element is clipped to the element's content box,
-		including both the paint of the descendants and their geometry</span>
+	1. The contents of the element must be clipped to the element's content box,
+		including both the paint of the descendants and their geometry.
+		<span class=note>This is similar to ''overflow: clip'',
+		but has no effect or dependency on the computed value of the 'overflow' property.</span>
+		This does not include the creation of any mechanism
+		to access or indicate the presence of the clipped content;
+		nor does it inhibit the creation of any such mechanism through other properties,
+		such as 'overflow', 'resize', or 'text-overflow'.
 	2. The element must act as a containing block for absolutely positioned and fixed positioned descendants.
 	3. The element must be a <a>stacking context</a>.
 	4. The element must be a <a>formatting context</a>.
@@ -293,8 +296,8 @@ Paint Containment</h3>
 		the UA can directly skip trying to paint its contents,
 		as they're guaranteed to be off-screen/obscured as well.
 
-	2. If the containing element's overflow has been changed to ''overflow/clip''
-		(because it was originally ''overflow/visible''),
+	2. Unless the clipped content is made accessible via a separate mechanism
+		such as the 'overflow', 'resize', or 'text-overflow' properties,
 		the UA can reserve "canvas" space for the element exactly the element's size.
 		(In similar, scrollable, situations, like ''overflow: hidden'',
 		it's possible to scroll to the currently-clipped content,

css-overflow/Overview.bs

@@ -29,8 +29,6 @@ type: dfn; spec:css-multicol-1; text:overflow column
 <pre class="anchors">
 url: https://www.w3.org/TR/2008/CR-css3-marquee-20081205/#the-overflow-style; type: property; text: overflow-style;
 url: https://drafts.csswg.org/selectors-3/#subject; type: dfn; text: subject;
-url: https://drafts.csswg.org/css-containment/#propdef-contain; type: property; text: contain
-url: https://drafts.csswg.org/css-containment/#paint-containment; type: dfn; text: paint containment
 </pre>
 	<style>
 		table.source-demo-pair {
@@ -392,15 +390,6 @@ Introduction</h2>
 				then computed values are the cascaded values
 				with ''overflow/visible'' changed to ''overflow/auto''.
 			</li>
-			<li>
-				Otherwise, if both cascaded values are ''overflow/visible''
-				and the computed value of 'contain' is
-				one that activates <a>paint containment</a>
-				(e.g. ''contain:strict''
-				or ''contain: paint''
-				or ''contain: layout paint''…),
-				then the computed values of both 'overflow-x' and 'overflow-y'
-				are changed to ''overflow/clip''.</li>
 			<li>
 				Otherwise, the computed values are as specified.
 			</li>