"?" at the end of an expression should probably be punctuation not "fill in the blank" in Nemeth

The following expression generates "fill in the blank":
```
 <math>
  <mrow data-changed='added'>
    <mrow data-changed='added'>
      <mn>2</mn>
      <mo>+</mo>
      <mi>x</mi>
    </mrow>
    <mo>?</mo>
  </mrow>
 </math>
```
Nemeth: ⠼⠆⠬⠭⠀⠿

It probably should be punctuation (⠦) for `?`