Displaystyle and mtable

Dear all,

There has been a change in the treatment of displaystyle on mtable in 
Gecko 29, while trying to remove some useless <mstyle> attributes and 
make things compatible with the CSS inheritance.

According to the MathML spec, the displaystyle attribute is compatible 
with the CSS inheritance:

"Some attributes, such as |displaystyle| or |scriptlevel| (explained 
below), are inherited from the surrounding context when they are not 
explicitly set. Specifying such an attribute on an |mstyle| element sets 
the value that will be inherited by its child elements. Unless a child 
element overrides this inherited value, it will pass it on to its 
children, and they will pass it to their children, and so on. But if a 
child element does override it, either by an explicit attribute setting 
or automatically (as is common for |scriptlevel|), the new (overriding) 
value will be passed on to that element's children, and then to their 
children, etc, unless it is again overridden. "

And for mtable, we have

"The |displaystyle| attribute is allowed on the |mtable| element to set 
the inherited value of the attribute. If the attribute is not present, 
the |mtable| element sets |displaystyle| to "false" within the table 
elements."

So as I read, the displaystyle is set to "true" on <mstyle> but set back 
to false on <mtable>.

     <math>
       <mstyle displaystyle="true">
         <mtable>
           <mtr>
             <mtd>
               <munder>
                 <mo>&Sum;</mo>
                 <mi>x</mi>
               </munder>
             </mtd>
           </mtr>
         </mtable>
       </mstyle>
     </math>

Gecko < 29 and MathJax 2.3 seems to keep displaystyle=true on the 
<munder> element (see attachment). It seems that other TeX-to-MathML 
converters (such as itex2MML or LaTeXML) assume that displaystyle won't 
be reset on <mtable>'s, so aligning on the spec causes a potential 
"regression" here. See also 
https://bugzilla.mozilla.org/show_bug.cgi?id=1011237

-- 
Frédéric Wang
maths-informatique-jeux.com/blog/frederic