\documentclass{article}
\usepackage{latexml}
\usepackage{amsmath}
\def\mockarray{\begin{array}{cc} 
  a & b \\
  c & d \end{array}}
\def\mockcases{\begin{cases}
  d & c \\
  b & a \end{cases}}
\begin{document}
% standalone cases 
\[\mockcases\]
% standalone array
\[\mockarray\]
   
% lbrace array 
\[\{ \mockarray\]
   
% rbrace array 
\[\mockarray \}\]
% matrix multiplication
\[ \mockarray \mockcases \]
% matrix in inequality
\[ a + b < \mockarray \]
% opfunction equation with piecewise matrix
\[ \arcsin \pi + \neg a = \{ \mockarray \]
\end{document}