"iq" and "presence" features

Hello from new ejabberd user!

I have a small question: ejabberd advertises two "interesting" features in disco#info: "iq" and "presence". What do they actually mean? (they are not mentioned at http://www.xmpp.org/registrar/disco-features.html). And then, why is there no "message" feature? (I think jabberd1.x publishes this one, too).

Just a note: the code is on

Just a note: the code is on mod_disco.erl lines 58-61:

    register_feature(Host, "iq"),
    register_feature(Host, "presence"),
    register_feature(Host, "presence-invisible"),
    register_feature(Host, "http://jabber.org/protocol/disco#publish"),
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