Feasibility of using LaTeXML for macro expansion

[andrewhead]

This issue is a stub for notes related to using LaTeXML to expand macros.

It's possible to listen for expansions of macros (those defined with \def) and commands (those defined with newcommand) in the gullet of LaTeXML. This much I have determined by setting breakpoints within the readXToken method of the gullet and inspecting the contents of the tokens read in, and the value of $r (i.e., the output of $def->invoke(...)) once those tokens are expanded.

However, this same approach doesn't seem to fully expand macros defined with the DeclareMathOperator command. Rather, it only partially expands them.