An updated internet-draft is available from the IETF.
Abstract: «The IMAPRev4 specification supports unsolicited responses being sent to a client at any time. The IDLE specification defines a way for a client to sit in an idle connection waiting to receive these responses. This document clarifies and extends the set of responses that a client may receive while in the idle state. The desire is to allow a client to predict exactly what set of unsolicited responses it can rely on receiving when listening on an idle connection.»