由于更新了 l3kernel、l3packages 和 l3experimental，我正在处理的 XeTeX 文档不再编译。我已将问题缩小到 fontspec 无法找到似乎之前可用的控制序列。最小工作示例如下：
\documentclass{article}
\usepackage{fontspec}
\setmainfont{Tinos}
\begin{document}
This is a minimal working example.
\end{document}
编译失败，日志如下：
This is XeTeX, Version 3.14159265-2.6-0.99992 (TeX Live 2015) (preloaded format=xelatex)
\write18 enabled.
entering extended mode
(./test.tex
LaTeX2e <2015/01/01> patch level 2
Babel <3.9l> and hyphenation patterns for 16 languages loaded.
(/home/pan/texlive/2015/texmf-dist/tex/latex/base/article.cls
Document Class: article 2014/09/29 v1.4h Standard LaTeX document class
(/home/pan/texlive/2015/texmf-dist/tex/latex/base/size10.clo))
(/home/pan/texlive/2015/texmf-dist/tex/latex/fontspec/fontspec.sty
(/home/pan/texlive/2015/texmf-dist/tex/latex/l3kernel/expl3.sty
(/home/pan/texlive/2015/texmf-dist/tex/latex/l3kernel/expl3-code.tex)
(/home/pan/texlive/2015/texmf-dist/tex/latex/l3kernel/l3unicode-data.def)
(/home/pan/texlive/2015/texmf-dist/tex/latex/l3kernel/l3xdvipdfmx.def))
(/home/pan/texlive/2015/texmf-dist/tex/latex/l3packages/xparse/xparse.sty)
(/home/pan/texlive/2015/texmf-dist/tex/latex/fontspec/fontspec-patches.sty)
(/home/pan/texlive/2015/texmf-dist/tex/latex/fontspec/fontspec-xetex.sty
(/home/pan/texlive/2015/texmf-dist/tex/latex/base/fontenc.sty
(/home/pan/texlive/2015/texmf-dist/tex/latex/euenc/eu1enc.def)
(/home/pan/texlive/2015/texmf-dist/tex/latex/euenc/eu1lmr.fd))
(/home/pan/texlive/2015/texmf-dist/tex/xelatex/xunicode/xunicode.sty
(/home/pan/texlive/2015/texmf-dist/tex/latex/tipa/t3enc.def
(/home/pan/texlive/2015/texmf-dist/tex/latex/euenc/eu1lmss.fd))
(/home/pan/texlive/2015/texmf-dist/tex/latex/graphics/graphicx.sty
(/home/pan/texlive/2015/texmf-dist/tex/latex/graphics/keyval.sty)
(/home/pan/texlive/2015/texmf-dist/tex/latex/graphics/graphics.sty
(/home/pan/texlive/2015/texmf-dist/tex/latex/graphics/trig.sty)
(/home/pan/texlive/2015/texmf-dist/tex/latex/latexconfig/graphics.cfg)
(/home/pan/texlive/2015/texmf-dist/tex/xelatex/xetex-def/xetex.def))))
(/home/pan/texlive/2015/texmf-dist/tex/latex/fontspec/fontspec.cfg)))
! Undefined control sequence.
<recently read> \str_case:nnn
l.3 \setmainfont{Tinos}
?