\documentclass{article}
\usepackage{latexml}
\usepackage{amsmath}
\begin{document}

\subsubsection{Empty Balanced}
\begin{enumerate}
  \item $()$
  \item $[]$
  \item $\{\}$
  \item $\langle\rangle$
  \item $\lfloor\rfloor$
  \item $\lceil\rceil$
  \item $()[]\{\}[]()$ % stacked empty
\end{enumerate}

\section{Advanced Fenced}
\begin{enumerate}
  \item $\langle a,b \rangle $ % list
  \item $\langle ab \rangle $ % unknown delimited
  \item $\langle a \rangle$ % unknown delimited
\end{enumerate}

\end{document}