Some TeXAtoms of class ORD don't get data-mjx-texclass="ORD" in serialized MathML output

[dpvc]

When TeXAtom nodes are created and setProperty('texClass') is NOT called for them, they get texClass of ORD automatically, but that isn't set in the property list, and so it doesn't appear in the serialized MathML output. That means that ORD class can be lost in saving to MathML and reading it back into MathJax. For example, when braces are used in TeX input, they produce a TeXAtom of class ORD of this type.

For example, f{\left(x\right)} currently produces

<math xmlns="http://www.w3.org/1998/Math/MathML">
  <mi>f</mi>
  <mrow>
    <mrow data-mjx-texclass="INNER">
      <mo data-mjx-texclass="OPEN">(</mo>
      <mi>x</mi>
      <mo data-mjx-texclass="CLOSE">)</mo>
    </mrow>
  </mrow>
</math>

and since the outer <mrow> does not include a TeX class, the spacing is that of INNER when this MathML is read into MathJax (but the spacing is ORD when the TeX input is processed).

The serialized MathML should produce

<math xmlns="http://www.w3.org/1998/Math/MathML">
  <mi>f</mi>
  <mrow data-mjx-texclass="ORD">
    <mrow data-mjx-texclass="INNER">
      <mo data-mjx-texclass="OPEN">(</mo>
      <mi>x</mi>
      <mo data-mjx-texclass="CLOSE">)</mo>
    </mrow>
  </mrow>
</math>