Question abot DTDDECL and SGMLDECL

Hi,

I hope, a few people are still reading this list :) My question: What
goes wrong? The docbook-xml SGML catalogs contain a DTDDECL entry

DTDDECL "-//OASIS//DTD DocBook XML V4.5//EN"
        "/usr/share/xml/declaration/xml.dcl"

If I do a

onsgmls -E1 -wxml -wall -gues test-4.5.xml

with a simple DB 4.5 XML file, it fails. If I add a SGMLDECL entry:

SGMLDECL "/usr/share/xml/declaration/xml.dcl"

it succeeds. Why does it fail in the first case? The PUBIDs are the same
in the DTDDECL and the testfile DOCTYPE. If there is some documentation
out there, that can explain my question, please don't hesitate to point
me to it.

Regards, Daniel