mathml/test_tex.tex

\documentclass{article}
% \usepackage{unicode-math}
\usepackage{amsmath}
\usepackage{luamml}
\RegisterFamilyMapping\symsymbols{oms}
\RegisterFamilyMapping\symletters{oml}
\RegisterFamilyMapping\symlargesymbols{omx}
\ExplSyntaxOn
\tracingmathml2
\pdfvariable compresslevel0
\cs_new_protected:Npn \ShowMathMLObj {
  \message { \luamml_get_last_mathml_stream:e{}~0~R }
}
\ExplSyntaxOff
\begin{document}
\[
  ax^2+bx+c=0
\]
\ShowMathMLObj
\[
  x = \frac{-b \pm \sqrt{b^2-4ac}}{2a}.
\]
\[
  \sum_a\underline c\dot bc'
\]

\begin{align}
  abc&=def & e^{\mathrm{i}\pi}&=-1\\
  1+2&=3\\
  5
\end{align}
\ShowMathMLObj

Es gilt $\sin(x)-\sin(x+2\pi)=0$.
\end{document}