[XeTeX] \hyphenation{} and combining diacritics

[maxwell]

This is a better answer than mine, so disregard my noise.  But I do have a
question below:

On Fri, 8 Jul 2011 23:13:41 +0200, Dominik Wujastyk <wujastyk at gmail.com>
wrote:
> ...
> There's also a command within XeTeX  that normalizes unicode
> before passing it to TeX's digestion.  Try this in your header:
> 
> % Normalize any residual Unicode combining accents,
> % and write out error messages, if any:
> \XeTeXinputnormalization=1
> \tracinglostchars=1
> \tracingonline=1

I found \XeTeXinputnormalization in XeTeX documentation, but I'm not
familiar with the other two commands.  I guess \tracingonline=1 means to
output errors to stdout (or stderr?), but where is the effect of
\tracinglostchars described?  In particular, what error msgs should I look
for if normalization fails or a font lacks a normalized character?

   Mike Maxwell