Sounds crazy, I used a wiki page Saturday and spent 5 hours trying to find it again so I can edit and add to it but I cannot. It may be LUA or SOFIA or ESL related. I found a page that had the names of variables I could get into a LUA program triggered by:
hook event="custom" subclass="sofia::unregister" script=“…..

There was a section for unregistered (and others) that list them like:
username: ….
from_user: ... 
I used them here:
local username  = event:getHeader("username");
local from_user = event:getHeader("from-user");

If anyone knows the page please point me to it. I found an item missing from the page and was going to edit the page and add it (missing user-agent for unregister event). I found this page:
https://freeswitch.org/confluence/pages/viewpage.action?pageId=15139388
and edited it but that’s not the one I originally saw, the other one had custom and other events for LUA listed. 
Thanks
Mario G