help with docbook in emacs using psgml

[Jack]

Hello all,

I had been using nxml mode in emacs (currently using 26.1) and was  
happy with it, except it generally said "invalid syntax" for most  
docbook files (which had no problems or errors with checkXML or  
meinproc5.  Today I tried to switch to psgml, but am unable to get  
syntax highlighting.   I have sgml-set-face and sgml-auto-activate-dtd  
both set to t, and sgml-markup-faces seems OK with what look like  
appropriate font-lock items.   Is there a useful set of instructions or  
tutorial?  I have hunted but not yet found anything helpful.  I would  
really prefer colored syntax highlighting, but it's not even clear to  
me if the font-lock faces will do that.

Thanks for any suggestions.

Jack