\documentclass[a4paper,twocolumn]{memoir}
\setlrmarginsandblock{2.5cm}*1
\checkandfixthelayout
\newoutputstream{showkeys}
\openoutputfile{\jobname.keys}{showkeys}
\addtostream{showkeys}{\protect\begin{description}}
\newcommand\felineMarkupDescription[5]{%
  \addtostream{showkeys}{\protect\item[#1] #2 }%
}
\usepackage[loadsampleconfig]{dlfltxbmarkup}
%\usepackage{dlfltxbmarkup}
\usepackage{calc,enumitem}
\setdescription{style=nextline,font=\ttfamily}
\addtostream{showkeys}{\protect\end{description}}
\closeoutputstream{showkeys}
\pagestyle{plain}
\addtolength\columnsep{1cm}
\setlength\columnseprule{0.4pt}
\begin{document}
\raggedright
\twocolumn[\section*{Key descriptions for the current setting of the
  \texttt{dlfltxbmarkup} package}]
\input{\jobname.keys}
\end{document}

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