Add the special case that '0 <length>' is equivalent to '0 0 <length>' for 'flex'.

--HG--
extra : rebase_source : a798730a7101391477a830717168d3e52afc3f51

Author: tabatkins

css3-flexbox/Overview.html

@@ -1389,6 +1389,14 @@ <h2 id=flexibility><span class=secno>7. </span> Flexibility: the ‘<a
    either be interpreted as as one of the flex ratios, or will make the
    declaration invalid.
 
+  <p> If the <a href="#positive-flexibility"><i>positive flex ratio</i></a>
+   is set to ‘<code class=css>0</code>’ and the <a
+   href="#negative-flex-ratio"><i>negative flex ratio</i></a> is omitted, the
+   latter defaults to ‘<code class=css>0</code>’ as well. <span
+   class=note>Note that this is different from the initial value of ‘<a
+   href="#flex-shrink"><code class=property>flex-shrink</code></a>’.</span>
+   
+
   <p> The keyword ‘<code class=property>none</code>’ computes to ‘<code
    class=css>0 0 auto</code>’.
 
@@ -1942,7 +1950,9 @@ <h3 id=flex-align><span class=secno>8.3. </span> Cross-axis Alignment: the
    class=css>auto</code>’</dfn> for ‘<a href="#flex-item-align"><code
    class=property>flex-item-align</code></a>’ computes to the value of
    ‘<a href="#flex-align0"><code class=property>flex-align</code></a>’ on
-   the element's parent. The alignments are defined as:
+   the element's parent, or ‘<a href="#flex-line-pack-stretch"><code
+   class=css>stretch</code></a>’ if the element has no parent. The
+   alignments are defined as:
 
   <dl>
    <dt><dfn id=flex-align-start>‘<code class=css>start</code>’</dfn>

css3-flexbox/Overview.src.html

@@ -902,6 +902,12 @@ <h2 id='flexibility'>
 		unitless zero will either be interpreted as as one of the flex ratios, 
 		or will make the declaration invalid.
 
+	<p>
+		If the <i>positive flex ratio</i> is set to ''0''
+		and the <i>negative flex ratio</i> is omitted,
+		the latter defaults to ''0'' as well.
+		<span class='note'>Note that this is different from the initial value of 'flex-shrink'.</span>
+
 	<p>
 		The keyword 'none' computes to ''0 0 auto''.