MakeUppercase 将字体规格功能名称大写

Question

对于扩展之前的\MakeUppercase更改，附加的 MWE 无法正常工作。FakeSlantFAKESLANT\addfontfeature

\documentclass{article}
\usepackage{fontspec}
\setmainfont{Erewhon}
\begin{document}
\MakeUppercase{my  {\addfontfeature{FakeSlant=0.4}italic} is slanted!}
\end{document}