Not working on Ubuntu 18.04

[tmalsburg]

This package used to work beautifully on Ubuntu. Thanks for sharing it! However, I'm now experiencing the following problem when I try to compile the hello world example shown in the README:

$ pdflatex test.tex 
This is pdfTeX, Version 3.14159265-2.6-1.40.18 (TeX Live 2017/Debian) (preloaded format=pdflatex)
 restricted \write18 enabled.
entering extended mode
(./test.tex
LaTeX2e <2017-04-15>
Babel <3.18> and hyphenation patterns for 12 language(s) loaded.
(/usr/share/texlive/texmf-dist/tex/latex/base/article.cls
Document Class: article 2014/09/29 v1.4h Standard LaTeX document class
(/usr/share/texlive/texmf-dist/tex/latex/base/size10.clo))
(/usr/share/texlive/texmf-dist/tex/latex/coloremoji/coloremoji.sty
(/usr/share/texlive/texmf-dist/tex/latex/graphics/graphicx.sty
(/usr/share/texlive/texmf-dist/tex/latex/graphics/keyval.sty)
(/usr/share/texlive/texmf-dist/tex/latex/graphics/graphics.sty
(/usr/share/texlive/texmf-dist/tex/latex/graphics/trig.sty)
(/usr/share/texlive/texmf-dist/tex/latex/graphics-cfg/graphics.cfg)
(/usr/share/texlive/texmf-dist/tex/latex/graphics-def/pdftex.def)))
(/usr/share/texlive/texmf-dist/tex/generic/oberdiek/stringenc.sty
(/usr/share/texlive/texmf-dist/tex/generic/oberdiek/infwarerr.sty)
(/usr/share/texlive/texmf-dist/tex/generic/oberdiek/ltxcmds.sty)
(/usr/share/texlive/texmf-dist/tex/generic/oberdiek/pdfescape.sty
(/usr/share/texlive/texmf-dist/tex/generic/oberdiek/pdftexcmds.sty
(/usr/share/texlive/texmf-dist/tex/generic/oberdiek/ifluatex.sty)
(/usr/share/texlive/texmf-dist/tex/generic/oberdiek/ifpdf.sty))))
(/usr/share/texlive/texmf-dist/tex/latex/l3packages/xparse/xparse.sty
(/usr/share/texlive/texmf-dist/tex/latex/l3kernel/expl3.sty
(/usr/share/texlive/texmf-dist/tex/latex/l3kernel/expl3-code.tex)
(/usr/share/texlive/texmf-dist/tex/latex/l3kernel/l3pdfmode.def)))
(/usr/share/texlive/texmf-dist/tex/latex/l3kernel/l3regex.sty
*****************************************************************
** 
** Package l3regex is obsolete and has been removed!
** 
** Its functionality is now only provided as part of the expl3 package.
** 
** The old packages will be removed entirely at the end of 2018.
** 
** Therefore, please replace '\usepackage{l3regex}'
** with '\usepackage{expl3}' in your documents as soon as possible.
** 
*******************************************************************

Package l3regex Warning: This package is obsolete --- use 'expl3' instead on in
put line 42.

) (/usr/share/texlive/texmf-dist/tex/latex/base/inputenc.sty
(/usr/share/texlive/texmf-dist/tex/latex/ucs/utf8x.def))
(/usr/share/texlive/texmf-dist/tex/latex/ucs/ucs.sty
(/usr/share/texlive/texmf-dist/tex/latex/ucs/data/uni-global.def))
(/usr/share/texlive/texmf-dist/tex/latex/adjustbox/adjustbox.sty
(/usr/share/texlive/texmf-dist/tex/latex/xkeyval/xkeyval.sty
(/usr/share/texlive/texmf-dist/tex/generic/xkeyval/xkeyval.tex
(/usr/share/texlive/texmf-dist/tex/generic/xkeyval/xkvutils.tex)))
(/usr/share/texlive/texmf-dist/tex/latex/adjustbox/adjcalc.sty)
(/usr/share/texlive/texmf-dist/tex/latex/adjustbox/trimclip.sty
(/usr/share/texlive/texmf-dist/tex/latex/collectbox/collectbox.sty)
(/usr/share/texlive/texmf-dist/tex/latex/adjustbox/tc-pdftex.def))
(/usr/share/texlive/texmf-dist/tex/latex/ifoddpage/ifoddpage.sty)
(/usr/share/texlive/texmf-dist/tex/latex/varwidth/varwidth.sty))
(/usr/share/texlive/texmf-dist/tex/latex/amsmath/amsmath.sty
For additional information on amsmath, use the `?' option.
(/usr/share/texlive/texmf-dist/tex/latex/amsmath/amstext.sty
(/usr/share/texlive/texmf-dist/tex/latex/amsmath/amsgen.sty))
(/usr/share/texlive/texmf-dist/tex/latex/amsmath/amsbsy.sty)
(/usr/share/texlive/texmf-dist/tex/latex/amsmath/amsopn.sty))
Runaway argument?
{
! Forbidden control sequence found while scanning use of \bool_if:nTF.
<inserted text> 
                \par 
l.36 \bool_if:nTF { \xetex_if_engine_p:
                                        || \luatex_if_engine_p: }
? 

Any ideas about what's wrong here and how I can fix this? Thank you!

[tmalsburg]

I tested PR #20 and it solved my problem partly. I also had to replace l3regex with expl3.