There are several docs pages about ejabberd:
I think that chat.html must be merged in Ejabberd.html page.
chat.html is the main reference, it should explain what you can do with the IM service on NethServer.
Ejabberd.html: do not consider it. It is an experimental alternative implementation of the “inline docs” for Nethgui. For instance:
We were trying to move inline help translations to Transifex, without success. The Cockpit based UI does not have such feature, so that kind of resources are considered obsolete.
nethserver-ejabberd.html is a developer-oriented document. It cannot be merged with the first one.