One of the Gajim developers pinged me this morning about a bug report in which Gajim is choking on an XMPP presence stanza that includes the child element <available>. Granted, "available" is not permitted XML character data for the element (per Section 2.2.2.1 of RFC 3921), but that's no reason for the client to choke. The Robustness Principle formulated by Jon Postel (see Section 1.2.2 of RFC 1122) states: "Be liberal in what you accept, and conservative in what you send." That applies to XMPP just as much to any other part of the Internet ecosystem. So ignore that value and file a bug report with the offending client project!