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

% punctExpr deliniates an "Expressions" (plural) production.
% Expressions is used only as a subordinate to ExpressionsNoBars,
% which in turn is a subordinate to the evalAtOp case of moreFactors

$ x | y,z,t $ 

\end{document}