Add note about the two categories of box-tree fixup, and their relative ordering. Fixes #1355.

Author: tabatkins

css-display/Overview.bs

@@ -622,6 +622,15 @@ Automatic Box Type Transformations</h3>
 	The root element’s display type is always <a>blockified</a>.
 	Additionally, a 'display' of ''display/contents'' computes to ''block'' on the root element.
 
+	Note: There are two methods used to fix up box types when a box is mismatched to its context.
+	One is transformation of the <a>computed value</a> of 'display', such as <a>blockification</a> and <a>inlinification</a> described here.
+	The other, taking place during [[#intro|box tree construction]] (after computed values have been determined),
+	is the creation of intermediary anonymous boxes,
+	such as happens in <a href="https://www.w3.org/TR/CSS2/tables.html#anonymous-boxes">tables</a>,
+	[[css-ruby-1#box-fixup|ruby]],
+	and <a href="https://www.w3.org/TR/CSS21/visuren.html#box-gen">flow</a> layout.
+
+
 <!--
 
 <h2 id='box-suppress'>