> Can anyone point me to any resources that talk about this mode?
I mention it in my book on SGML Tools (but not in detail) and it's
on the CD-ROM. It requires make-regexp.el (in the distribution,
and some documentation). I use it all the time, it's great.
Local copy at: ftp://ftp.ucc.ie/pub/sgml/omnimark-mode.tar.gz