Created attachment 176896 [details]
bevelled.odt

Hello there. I'm writing this issue on behalf of ONLYOFFICE DocumentServer team (https://github.com/ONLYOFFICE/DocumentServer)

During the development of our product, we think we found some problem with rendering MathML formula with `mfrac` attribute `bevelled`

See attached document:

It has two objects:

Object 2/content.xml with:

<math xmlns="http://www.w3.org/1998/Math/MathML">
<semantics>
<mfrac>
<mrow>
<mn>1</mn>
</mrow>
<mrow>
<mn>2</mn>
</mrow>
</mfrac>
</semantics>
</math>

And 

Object 3/content.xml with:
<math xmlns="http://www.w3.org/1998/Math/MathML" display="block">
<semantics>
<mfrac bevelled="true">
<mrow>
<mn>1</mn>
</mrow>
<mrow>
<mn>2</mn>
</mrow>
</mfrac>
</semantics>
</math>

So this formula differs that the first one has no `bevelled` (and this is false by default) and second one has bevelled="true")

But on render both those formulas looks like the same

According to https://www.w3.org/TR/MathML3/chapter3.html
this attribute used for display formulas like this:

> Specifies whether the fraction should be displayed in a beveled style (the numerator slightly raised, the denominator slightly lowered and both separated by a slash), rather than "build up" vertically

I don't know if this worked at all in the previous build of LibreOffice, so I'm marking this as enhancement 

My Eniroment:
Kubuntu 20.04
LibreOffice flatpak 7.2.3.2