[css-display-3] Incorporate Oriol's proposed sentence about box relationships. #3158

Author: fantasai

css-display-3/Overview.bs

@@ -85,13 +85,6 @@ Introduction</h2>
 	cause the [=CSS/element=] and/or its descendants to not generate any <a>boxes</a> at all.
 	<a>Boxes</a> are often referred to by their 'display' type--
 	e.g. a <a>box</a> generated by an element with ''display: block'' is called a “block box” or just a “block”.
-	The <dfn export for=CSS>parent box</dfn> of an element’s <a>principal box</a>
-	is, in general,
-	the <a>principal box</a> of its nearest ancestor element
-	that generates a <a>box</a>;
-	there are exceptions for ''run-in'' boxes,
-	display types that generate multiple boxes (such as tables),
-	and intervening <a>anonymous boxes</a>.
 
 	A <a>box</a> is assigned the same styles as its generating [=CSS/element=], unless otherwise indicated.
 	In general, <a>inherited properties</a> are assigned to the <a>principal box</a>,
@@ -115,6 +108,19 @@ Introduction</h2>
 	which is assigned the same styles as the generating <a>text nodes</a>.
 	If the sequence contains no text, however, it does not generate a <a>text run</a>.
 
+	In constructing the box tree,
+	boxes generated by an element are descendants of
+	the principal box of any ancestor elements.
+	In general,
+	the direct <dfn export for=CSS>parent box</dfn>
+	of an element’s <a>principal box</a>
+	is the <a>principal box</a>
+	of its nearest ancestor element that generates a <a>box</a>;
+	however, there are some exceptions,
+	such as for ''run-in'' boxes,
+	display types that generate multiple container boxes (such as tables),
+	and intervening <a>anonymous boxes</a>.
+
 	An <dfn id="anonymous" oldids="css-anonymous" for=CSS lt="anonymous|anonymous box" export>anonymous box</dfn> is a box that is not associated with any element.
 	<a>Anonymous boxes</a> are generated in certain circumstances
 	to fix up the <a>box tree</a> when it requires a particular nested structure