DocBook 5.2 DTD missing - Generating .dtd from Relax NG doesn't work

[jodekirk]

A major roadblock to adopting the newer DocBook 5.1, and 5.2 is lack of XML editor support, mostly because there isn't a newer DTD available.

I use XMetaL 19 and Altova Authentic and they do not support Relax NG or Schematron. I asked tech support and they have added the request to their new feature request list.

XMetaL 19 supports DocBook 5.0 DTD with XInclude as docbookxi.dtd.

I tried to generate the newest 5.2 .dtd files from the Relax NG, but the Trang program has errors:
I used the Relax NG files here: https://docs.oasis-open.org/docbook/docbook/v5.2/os/rng/
https://docs.oasis-open.org/docbook/docbook/v5.2/os/rng/docbookxi.rng

Can somebody please generate the 5.2 version of the docbookxi.dtd files and share?