\input regression-test.tex
\documentclass{article}
\usepackage{semcat}

\begin{document}
\START

\begin{SemCatExplain}[category=B]{An example explanation}
Supplementary background that a reader could skip.
\end{SemCatExplain}
\TYPE{after-explain=reached}

\begin{SemCatExplain}[category=B,mode=slides]{Hidden without modes}
This should still typeset unconditionally, since osglecture-modes is
not loaded here and an unresolved mode key is simply ignored.
\end{SemCatExplain}
\TYPE{after-explain-with-mode-key=reached}

\clearpage
\listof{semcatexplain}{List of Explanations}

\TYPE{done=yes}
\END
\end{document}