description of overflow debug facility

layout/doc/frame_reflow_debug.html

@@ -27,6 +27,7 @@ start of its reflow
 <li>max. element size (MES) width
 <li>maximum Width
 <li>frame status
+<li>overflow area
 </ul>
 
 <h2>Getting the log</h2>
@@ -147,7 +148,9 @@ The table cell requires its children to compute the MES. It is reported back fro
 The block has been required to compute the max. element size only once and it reports now:
 <p> <code class="log">block 02D7BCF8 d=1410,300</code></p>
 <p>The block shows the same address as the previous one. 
-The reflow finishes at the same level where it started.
+<p>Frames with children that overflow  the parent have the <code>NS_FRAME_OUTSIDE_CHILDREN</code> flag set. For these frames 
+the overflowarea  is displayed as  <code class="log">block 025ED8F0 d=8940,1020 o=(0,0) 9180 x 1020</code>. The overflow area is specified as (x,y) origin and width x height.
+<p> The reflow finishes at the same level where it started.
 
 <h2>Advanced reflow debugging</h2>
 <p>The previously described technique dumps the data for every frame. Sometimes the log is clearer if only the main frames are shown.