DOCBOOK-APPS: DTD validation question for docbook under redhat

["Robert P. J. Day" <rpjday@mindspring.com>]

  i was playing around on the latest red hat beta -- limbo --
and for the fun of it, decided to see what would happen if i
tried to define my docbook file with an invalid DTD number, so
i cranked the value in the public and system identifiers up
to 4.3, which does not exist -- limbo comes with 4.2.

  no problem, xsltproc generated the HTML just fine, so i'm
curious, what's the algorithm for locating the proper DTD when
xslsproc goes to work?  as i read it, that program uses the
contents of the env var SGML_CATALOG_FILES, but that still
doesn't explain why there was no complaint about a non-existent
DTD file.

  comments?

rday