<math xmlns="&mathml;">
<mrow>
<msubsup>
    <mi>J</mi>
    <mrow><mi>i</mi><mi>j</mi></mrow>
    <mrow><mi>&alpha;</mi><mi>&beta;</mi></mrow>
</msubsup>
<msup>
   <mi>S</mi>
   <mi>&alpha;</mi>
</msup>
</mrow>
</math>

In this example, because of the algorithm described in
https://w3c.github.io/mathml-core/#base-with-subscript-and-superscript
the superscripts have different baselines, in a way which harms readability (in my opinion).
I would be interested to see if an alternative algorithm could try find a SuperShift (SubShift) for the row in it's entirety, and so show the scripts on consistent baselines across the row.