Embedding the semantic tree in MathML

OP on mathjax-dev

Starting example: a+b+c which might be realized as

<math>
  <mi>a</mi>
  <mo>+</mo>
  <mi>b</mi>
  <mo>+</mo>
  <mi>c</mi>
</math>

which would yield [a semantic tree](https://github.com/zorkow/speech-rule-engine/blob/sloan_branch/doc/grammar.tex] looking like

+ 
|--- a
|--- b
|--- c

which could be embedded as follows

<math>
  <mrow data-math-semantic-parent="sum" data-math-semantic-children="3">
     <mi data-math-semantic-child>a</mi>
     <mo data-math-semantic-operator>+</mo>
     <mi data-math-semantic-child>b</mi>
     <mo data-math-semantic-operator>+</mo>
     <mi data-math-semantic-child>c</mi>
  </mrow>
</math>

In other words,

• add mrows when necessary for semantic-tree-nodes with children
• identify children
• do some countin.

The hope is that this simple parent/child structure works well recursively, e.g.,

a + b*d + c

i.e.,

<math>
  <mi>a</mi>
  <mo>+</mo>
  <mi>b</mi>
  <mo>&#x22C5;</mo>
  <mi>d</mi>
  <mo>+</mo>
  <mi>c</mi>
</math>

would lead to a semantic tree of

+ 
|--- a
|--- *
|    |--- b
|    |--- c
|--- d

and we simply start from the leafs adding an mrow for * etc. to get

<math>
<mrow  data-math-semantic-parent="sum" data-math-semantic-children="3">
  <mi  data-math-semantic-child> a</mi>
  <mo  data-math-semantic-operator>+</mo>
  <mrow  data-math-semantic-parent="product" data-math-semantic-children="2">
    <mi data-math-semantic-child>b</mi>
    <mo data-math-semantic-operator>&#x22C5;</mo>
    <mi data-math-semantic-child>d</mi>
  </mrow>
  <mo data-math-semantic-operator>+</mo>
  <mi data-math-semantic-child>c</mi>
</mrow>
</math>

This is assuming the MathML tree numbering (IDs) that Neil, Davide and the folks at Texthelp designed.

Questions:

• Is this too simplistic?
• Is adding mrows too destructive?
• Do we need/want to be more destructive than that?