Hi Enrico, The following source causes an error on pLaTeX and upLaTeX.
! Bad character code (42146). \char_value_catcode:n ...val:w #1\__int_eval_end:
l.19 \xpatchcmd*{\hoge}{ほげ}{ふが}{}{} ^^M A character number must be between 0 and 255. I changed this one to zero.
% ====== \documentclass{article} \usepackage{regexpatch} \def\hoge{ああ，ほげとほげがぴよ。} \begin{document} Before: \hoge \xpatchcmd*{\hoge}{ほげ}{ふが}{}{} After: \hoge \end{document} % ====== (e-)(u)pTeX does not allow character code > 255 for \catcode, \sfcode, etc. For the time being, we can avoid the error by adding empty braces at the beggining like \def\hoge{{}ああ，ほげとほげがぴよ。} but I hope the issue can be resolved on the package. Best, Hironobu --- Hironobu YAMASHITA (GitHub: @aminophen)