Xy4DOS's original release in 12/91 was a very messy event. The product (Sig) preceded some of the manuals by about four months or so. And that wasn't all. XyQuest promoted the product as something radically new, operated by menus; I vividly recall the first few Emails from the SysOp at the BBS, which didn't even acknowledge that Sig could be customized, or made to operate almost like Xy3. Took months of tooth-pulling to extract the facts, and always in bits & pieces -- never a coherent view.
At some point Christine Madsen (or Bob Bamford?), in response to really LOUD howls & protests, posted to me a file that describes, in detail, how the Menu system (HLP MNU DLG U2 etc) is constructed.
Caution! This is an early, almost prehistoric explanation. There have been elaborations (but few alterations) to the way Help works. The doc may contain obsolete info here & there (haven't looked at this in a while); but 99.99% of Signature is still alive in XyWin, so this should supply much of what is (unaccountably) missing in XyWin docs.