Here a long overdue and promised update on my work on libpurple's XMPP protocol plugin.

Currently I'm finishing support for XEP-0115 version 1.5 in the protocol plugin. I've decided to only support latest version of the XEP because it's most secure. However, what does this mean exactly?

Well, former caps worked so you give a version string and so called short names with your presence stanzas. Though shortnames are really obsolete and we already have a registry for features identified by their namespace and the former version of the protocol didn't provide any amount of security. One could tell you that it's Psi or Tkabber and send a whole different feature set and all clients with that version would be associated with the wrong feature set of the poisoned cache.