Using ProGuard with Xerces

After a long and futile search, I have nothing left but to repeat this
(unanswered) question (not by me) from Jun 2003:

I am trying to use Proguard (obfuscator-shrinker) on a program that
uses Xerces-J. I am finding it quite painful to create, by trial and
error, the list of methods/classes that need to be kept even if
ProGuard does not detect their being used.
Has anyone already dealt with this ? Did someone already establish a
list of methods/classes that obfuscators do not recognize as being
used but should be kept anyway ?

Thanks in advance,
Viktor.