
<https://www.w3.org/TR/MathML3/>

<https://en.wikipedia.org/wiki/MathML>

"Strict Content MathML" is a subset, compatible with Open Math (which is itself an XML encoding).

Systems Biology Markup Language (SBML) is another XML schema for representing
models of biological systems and chemical reactions.
=> <http://sbml.org/More_Detailed_Summary_of_SBML>

There are a bunch of non-printing "entities" (characters) with Unicode mappings:

U+2061 FUNCTION APPLICATION;
U+2062 INVISIBLE TIMES;
U+2063 INVISIBLE SEPARATOR;
U+2064 INVISIBLE PLUS;


Presumably, we'll want to support reading *content* MathML, and output eithr
content or presentation.