[css-contain][css-overflow-4] refactoring

Move interaction between contain and fragmentation of overflow to
the css-overflow-4 specification

Closes #1374

Author: frivoal

css-contain/Overview.bs

@@ -225,10 +225,6 @@ Layout Containment</h3>
 				of the region which traps the content
 				is set to ''overset'' if the content doesn't fit,
 				even if it is not the last region in the region chain.
-			- If the computed value of the 'continue' property
-				on an element with <a>layout containment</a>
-				would otherwise have been ''continue/auto'' or ''continue/fragments'',
-				it must instead compute to ''continue/overflow''.
 
 	3. If the contents of the element overflow the element,
 		they must be treated as <a>ink overflow</a>.
@@ -401,6 +397,7 @@ This appendix is <em>informative</em>.
 <ul>
 	<li>Clarify the interaction with display: contents
 	<li>Clarify how containment works on table parts
+	<li>Move the interaction between containment and fragmentation of overflow from this specification to CSS-OVERFLOW-4
 </ul>
 
 <h3 id="fpwd-changes">Changes from the

css-overflow/Overview.bs

@@ -450,7 +450,10 @@ while ''continue: paginate'' replaces "overflow: paged-x | paged-y | paged-x-con
 
 The computed value of the 'continue' for a given element or pseudo element is determined as follow:
 <ol>
-	<li>If the specified value is ''continue/auto''
+	<li>On elements or pseudo elements with <a>layout containment</a> (see [[!CSS-CONTAIN-1]]),
+	if the specificied value is ''continue/auto'' or ''continue/fragments''
+	then the computed value is ''continue/overflow''.
+	<li>Otherwise, if the specified value is ''continue/auto''
 	<ol>
 		<li>On a <a spec="css-regions">CSS Region</a> other than the last one in a <a spec="css-regions">region chain</a>,
 		the computed value is ''continue/auto''
@@ -460,7 +463,7 @@ The computed value of the 'continue' for a given element or pseudo element is de
 		the computed value is ''continue/fragments''
 		<li>Otherwise, the computed value is ''continue/overflow''
 	</ol>
-	<li>If the specified value is ''continue/framgents''
+	<li>Otherwise, if the specified value is ''continue/framgents''
 	<ol>
 		<li>On a page
 		the computed value is ''continue/paginate''