For this MWE, run with xelatex in TexLive 2020 on Windows 10:
\documentclass{article}
\usepackage{makeidx}
\usepackage{hyperref}
\makeindex
\begin{document}
\index{foo} % OK, but without this line, the .idx file is empty
\index{Sibelius!Difference between Sibelius "| First and Sibelius "| Ultimate}
\printindex
\end{document}
The .idx
file (given below) is wrong. Apparently something has misinterpreted the second "|
as a "
character followed by a pagenumber-formatting |
command.
\indexentry{foo|hyperpage}{1}
\indexentry{Sibelius!Difference between Sibelius "|hyperindexformat{\ First and Sibelius "}}{1}
makeindex
then gives the error message
!! Input index error (file = test.idx, line = 2):
-- Incomplete first argument (premature LFD).
(Note: IMHO the decision of a software company to name three versions of an app as "Sibelius", "Sibelius | First" and "Sibelius | Ultimate", using the vertical bar characters and spaces exactly as shown, is moronic, but that's what they have done!)