\documentclass{standalone}
\usepackage{luamplib}
\begin{document}
\begin{mplibcode}
beginfig(1);
string s; s = "\TeX\ sets maths like this $e=mc^2$";
draw ("1. " & s) infont defaultfont;
draw ("2. " & s) infont "texnansi-lmr10" shifted 20 down;
draw ("3. " & s) infont "cmtt10" shifted 40 down;
draw ("4. " & s) infont "texnansi-lmtt10" shifted 60 down;
bboxmargin := 14;
picture p; p = currentpicture;
fill bbox currentpicture withcolor (1,1,31/32);
draw p; draw bbox p;
endfig;
\end{mplibcode}
\end{document}
end.