Excess vertical space in \vdots

Question

How do I get a tight \fbox around \vdots? There is an excess vertical space as discussed in

• Vertical space around \vdots in xymatrix
• Wrong (too much) vertical space above \vdots in small matrix

The code below produces:

Code:

\documentclass{article}

%% Defined in https://tex.stackexchange.com/a/412418/4301
\newcommand{\myvdots}{\raisebox{.006\baselineskip}{\ensuremath{\vdots}}}

\begin{document}
p
\fboxsep=0pt\fbox{\vdots}
\fboxsep=0pt\fbox{\myvdots}
y
\end{document}

Answer 1

The definition of \vdots in fontmath.ltx reads

\DeclareRobustCommand
  \vdots{\vbox{\baselineskip4\p@ \lineskiplimit\z@
    \kern6\p@\hbox{.}\hbox{.}\hbox{.}}}

(This is inherited from plain.tex with the addition of robustness.) I don't quite know the idea behind the \kern6\p@ bit, but removing it removes the excess box height

\documentclass{article}

\makeatletter
\DeclareRobustCommand
  \myvdots{\vbox{\baselineskip4\p@ \lineskiplimit\z@
    \hbox{.}\hbox{.}\hbox{.}}}
\makeatother

\begin{document}

\fboxsep=0pt
p \fbox{\vdots} \fbox{\myvdots} y

\end{document}