\documentclass{article}

\usepackage{rail}

\railoptions{-t}

\relax

\begin{document}

\verb!\\!
\begin{rail}
\\
\end{rail}

\verb!x \\!
\begin{rail}
x \\
\end{rail}

\verb!\\ x!
\begin{rail}
\\ x
\end{rail}

\verb!x \\ y!
\begin{rail}
x \\ y
\end{rail}

\verb!\\ | x \\ | \\ y | x \\ y!
\begin{rail}
\\ | x \\ | \\ y | x \\ y
\end{rail}

\verb!x +!
\begin{rail}
x +
\end{rail}

\verb!\\ +!
\begin{rail}
\\ +
\end{rail}

\verb!\\ + \\!
\begin{rail}
\\ + \\
\end{rail}

\verb!\\ *!
\begin{rail}
\\ *
\end{rail}

\verb!\\ * \\!
\begin{rail}
\\ * \\
\end{rail}

\verb!\\ ?!
\begin{rail}
\\ ?
\end{rail}

\verb!(x *)!
\begin{rail}
x *
\end{rail}

\end{document}