Very nice! One thing I've found useful about MathML is that, since it's XML, it's easy to generate (e.g. from scripts) and transform (e.g. with XSLT).

My preferred workflow at the moment is to programatically-generate "Content MathML", which lets me focus on the structure of things (akin to Lisp's prefix-form s-expressions), e.g. here's "applying plus to identifier x and identifier y":

    <apply>
      <csymbol definitionURL="https://openmath.org/cd/arith1#plus">plus</csymbol>
      <ci>x</ci>
      <ci>y</ci>
    </apply>

Browsers can't display Content MathML, so I use XSLT (adapted from [1]) to convert it to "Presentation MathML". The "MathML Core" discussed in this article is a subset of Presentation MathML. Presentation MathML focuses on the layout of symbols, e.g. the above becomes "identifier x followed by operator + followed by identifier y":

    <mrow><mi>x</mi><mo>+</mo><mi>y</mi></mrow>

This separation also lets me choose different notations, without having to alter the underlying data; e.g. on this page which compares two different notations http://www.chriswarbo.net/projects/units/negative_bar_notati... (if you click the "View Source" link at the bottom, you'll see the same data being piped into `math block` and `math block minus`, which just apply a different stylesheet).

[1] https://www.w3.org/Math/XSL/Overview-tech.html