Is it possible to have an vertical line which covers the second environment to mark the indent? I have no idea how to do that and would be grateful for any hint. Thanks a lot.
\documentclass[12pt]{scrartcl}
\usepackage{enumitem}
\begin{document}
\begin{description}
\item[A] ooo
\begin{description}
\item[1] xxx
\item[2] xxx
\end{description}
\item[B] ooo
\end{description}
\end{document}