[css-contain] Clarify scoping properties to subtrees

Closes w3c#2349

Author: frivoal

css-contain-1/Overview.bs

@@ -281,7 +281,10 @@ Style Containment</h3>
 	and vice versa.
 	If scoped to a sub-tree, it's the same,
 	except the scoping element itself is counted as "outside" the tree,
-	like the rest of the document.
+	like the rest of the document,
+	and the effects of the property on that element are unaffected by scoping.
+	When considering the effects of the scoped property on elements <em>inside</em> the subtree,
+	the element at the base of the subtree is treated as if it was the root of the document.
 
 	When scoped, the 'counter-set' and 'counter-increment' <a spec=css-lists-3>create a new counter</a>.
 
@@ -453,6 +456,7 @@ This appendix is <em>informative</em>.
 	<li>Align paint containment's behavior with overflow:clip
 	<li>Elements with size containment are monolithic
 	<li>Forced breaks area allowed in elements with layout containments, but do not propagate
+	<li>Clarify the effects of scoping to a subtree
 </ul>
 
 <h3 id="2017-04-19-changes">Changes from the

css-contain-1/issues-2017-cr.html

@@ -105,13 +105,14 @@ <h1>CSS Contain Level 1 Disposition of Comments for 2017-02-21 WD</h1>
 Comment:  <a href='https://github.com/w3c/csswg-drafts/issues/2483#issuecomment-377214307'>https://github.com/w3c/csswg-drafts/issues/2483#issuecomment-377214307</a>
 Response: <a href='https://github.com/w3c/csswg-drafts/issues/2483#issuecomment-379124749'>https://github.com/w3c/csswg-drafts/issues/2483#issuecomment-379124749</a>
 Open</pre>
-<pre class=' open' id='issue-9'>
+<pre class='a' id='issue-9'>
 Issue 9. <a href='#issue-9'>#</a>
 Summary:  Clarify style containment property scopment
 From:     Oriol Brufau
 Comment:  <a href='https://github.com/w3c/csswg-drafts/issues/2349'>https://github.com/w3c/csswg-drafts/issues/2349</a>
 Response: <a href='https://github.com/w3c/csswg-drafts/issues/2349#issuecomment-379127071'>https://github.com/w3c/csswg-drafts/issues/2349#issuecomment-379127071</a>
-Open</pre>
+Closed:   Accepted
+Resolved: <a href='https://github.com/w3c/csswg-drafts/issues/2349#issuecomment-380361614'>https://github.com/w3c/csswg-drafts/issues/2349#issuecomment-380361614</a></pre>
 <pre class='a' id='issue-9'>
 Issue 9. <a href='#issue-9'>#</a>
 Summary:  Applicability of size contaiment to non atomic inlines

css-contain-1/issues-2017-cr.txt

@@ -81,7 +81,8 @@ Summary:  Clarify style containment property scopment
 From:     Oriol Brufau
 Comment:  https://github.com/w3c/csswg-drafts/issues/2349
 Response: https://github.com/w3c/csswg-drafts/issues/2349#issuecomment-379127071
-Open
+Closed:   Accepted
+Resolved: https://github.com/w3c/csswg-drafts/issues/2349#issuecomment-380361614
 ----
 Issue 9.
 Summary:  Applicability of size contaiment to non atomic inlines