[css-contain] Define behavior on table parts

Author: frivoal

css-contain/Overview.bs

@@ -155,6 +155,7 @@ Types of Containment</h2>
 Size Containment</h3>
 
 	If the element does not generate a <a>principal box</a> (as is the case with ''display: contents'' or ''display: none''),
+	or if the element is an <a spec="css-display-3">internal table element</a>,
 	size containment has no effect.
 	Otherwise, giving an element <dfn export>size containment</dfn> has the following effect:
 
@@ -192,6 +193,7 @@ Size Containment</h3>
 Layout Containment</h3>
 
 	If the element does not generate a <a>principal box</a> (as is the case with ''display: contents'' or ''display: none''),
+	or if the element is an <a spec="css-display-3">internal table element</a> other than ''display: table-cell'',
 	layout containment has no effect.
 	Otherwise, giving an element <dfn export>layout containment</dfn> has the following effects:
 
@@ -287,6 +289,7 @@ Style Containment</h3>
 Paint Containment</h3>
 
 	If the element does not generate a <a>principal box</a> (as is the case with ''display: contents'' or ''display: none''),
+	or if the element is an <a spec="css-display-3">internal table element</a> other than ''display: table-cell'',
 	paint containment has no effect.
 	Otherwise, giving an element <dfn export>paint containment</dfn> has the following effects:
 
@@ -335,6 +338,7 @@ This appendix is <em>informative</em>.
 
 <ul>
 	<li>Clarify the interaction with display: contents
+	<li>Clarify how containment works on table parts
 </ul>
 
 <h3 id="fpwd-changes">Changes from the