Clarify emptiness wrt margin box layout rules. <http://www.w3.org/mid/20110919211436.GC20209@bowman.infotech.monash.edu.au>

--HG--
extra : rebase_source : 81944f02842d5188be0341d7a6a5ee5f3066b121

Author: fantasai

css3-page/Overview.html

@@ -1404,15 +1404,13 @@ <h4 id=margin-dimension><span class=secno>6.3.2. </span>Margin Box
       <li>The sum of the outer widths of the three boxes is equal to max box
        width. (Margin box margins do not collapse.)
 
-      <li>If the center box is not empty or if its computed width is not
-       ‘<code class=property>auto</code>’, then the outer widths of the
-       other two boxes are equal to each other (i.e., the center box is
-       centered in that case).
-
-      <li>If a box is empty and its computed width is ‘<code
-       class=property>auto</code>’, then the used values of its left and
-       right padding width and left and right border width are all 0. (This
-       makes such a box invisible, because, by item 5, its width is also 0.)
+      <li>If the center box exists, then the outer widths of the other two
+       boxes are equal to each other (i.e., the center box is centered in
+       that case).
+
+      <li>If a margin box is not generated, then the used values of its
+       width, left and right padding, and left and right border width in
+       these formulas are all 0.
 
       <li>The used values of the margin boxes' left and right margins are
        their respective computed values, unless the respective computed value

css3-page/Overview.src.html

@@ -1005,12 +1005,12 @@ <h4 id="margin-dimension">Margin Box Variable Dimension Computation Rules</h4>
   <ol>
     <li>The sum of the outer widths of the three boxes is equal to max box width.
       (Margin box margins do not collapse.)</li>
-    <li>If the center box is not empty or if its computed width is not 'auto', then
+    <li>If the center box exists, then
     the outer widths of the other two boxes are equal to each other (i.e., the
     center box is centered in that case).</li>
-    <li>If a box is empty and its computed width is 'auto', then the used values of
-    its left and right padding width and left and right border width are all 0.
-    (This makes such a box invisible, because, by item 5, its width is also 0.)</li>
+    <li>If a margin box is not generated, then the used values of
+    its width, left and right padding, and left and right border width
+    in these formulas are all 0.
     <li>The used values of the margin boxes' left and right margins are their
     respective computed values, unless the respective computed value is 'auto'.</li>
     <li>If a box's computed width is 'auto', then its used width must be greater