Most of RFC 3921 is supported, with the following exceptions.
Messages of type “headline” are not treated in any special way.
<thread/> element is not used or generated.
Sending “directed presence” is supported; however, presence stanzas received from contacts not in roster are ignored.
Privacy lists are not supported at all.
jabber.el doesn't support XMPP-E2E or “im:” CPIM URIs.