[XeTeX] Character height and depth question

[Stephen Moye]

If I typeset the following:

%&program=xetex

\font\title="Zapfino" at 24pt \title

\parindent=0pt

\def\reverseit#1{\setbox0=\hbox{\enskip%
\special{color push}\special{color cmyk 0 0 0 0}#1\special{color pop}\quad}%
\leavevmode\hbox to 0pt{\special{color push}\special{color cmyk 0 1 1 .2}%
\vrule width\wd0 height\ht0 depth\dp0 \hss\special{color pop}}%
\box0}

\noindent \reverseit{SDFH} \qquad \reverseit{Big ypqjkl}

\bye

%#%#%#%#%#%

I seem to end up with constant  height or depth of a box containing a character, rather than being dependent on the actual depth of the character. Is there some way to find out what the real height and depth of a character, or is this a limitation of AAT and OT fonts?

Thanks for any insights.

Stephen Moye

PS -- Apologies if this message shows up twice. I sent it earlier today and it never showed up. Odd.