Typesetting the vertical line tone marking used in Pe̍h-ōe-jī
You can stack a rule with appropriate dimensions over the character:
\documentclass{article}
\newcommand{\vla}{}% for safety
\DeclareRobustCommand{\vla}[1]{%
\leavevmode\vbox{%
\offinterlineskip
\ialign{##\cr
\hidewidth\rule{0.08ex}{0.45ex}\hidewidth\cr
\noalign{\vskip0.2ex}
#1\cr
}%
}%
}
\begin{document}
P\vla{e}h-\={o}e-j\={\i}
\end{document}
\documentclass{article}
\usepackage{lmodern}
\usepackage{stackengine}
\newcommand\myaccent[1]{%
\stackengine{-.45ex}{#1}{\scriptsize\textquotesingle}{O}{c}{F}{T}{S}}
\begin{document}
P\myaccent{e}h-\={o}e-j\={i}
P\myaccent{E}H-\={O}E-J\={I}
\end{document}