\input{umtest-preamble} \usepackage{unicode-math} \setmathfont{xits-math.otf} \setmathfont[version=bold,Colour=009900]{xits-math.otf} \begin{document} \[ (x+y)^{{z+c}^{a+b}} \] \mathversion{bold} \[ (x+y)^{{z+c}^{a+b}} \] \end{document}