[css-pseudo] Actually drop a dfn for 'tree-abiding'.

Author: tabatkins

css-pseudo/Overview.bs

@@ -633,7 +633,7 @@ Security and Privacy Considerations</h3>
 <h2 id="treelike">
 Tree-Abiding Pseudo-elements</h2>
 
-  These pseudo-elements always fit within the box tree.
+  <dfn lt="tree-abiding|tree-abiding pseudo-element">Tree-abiding pseudo-elements</dfn> always fit within the box tree.
   They <a lt="inheritance">inherit</a> any inheritable properties from their <a>originating element</a>;
   non-inheritable properties take their <a>initial values</a> as usual.
   [[CSS3CASCADE]]