%%% \vbox height vs. \vtop depth

% \vbox usually inherits its depth from the last box or rule of the vertical
% list it contains. Conversely, \vtop has usually the height of the first box
% or rule of the vertical list it contains. However, using whatsits as the
% first/last item of the box may lead to surprises.

\def\what{\special{}}
\setbox0=\vbox{Aqq \what} \the\ht0, \the\dp0
\setbox0=\vtop{\what Aqq} \the\ht0, \the\dp0

% \vbox still obeys the rule, although there is a whatsit after the very
% last box on the list. But \vtop has always zero height if its first item is a
% whatsit.

\end