Peter Hutterer, the Red Hat input expert responsible for much of the multi-touch support and MPX support in X.Org, blogged this morning at first about Multitouch in X - Getting events. In that first post he outlines how to identify touch devices and register for touch events using the X Input 2.2 extension. Unless you're into low-level input handling, this read won't be of interest to you.
Peter immediately followed up with another X multi-touch blog post, but the next one is about pointer emulation. Pointer emulation in X.Org is for generating pointer events based upon a sequence of touch events. "The conditions for emulation are that the the touch sequence is eligible for pointer emulation and that no other client has a touch selection on that window/grab."
Peter additionally explains, "One of the base requirements of adding multitouch support to the X server was that traditional, non-multitouch applications can still be used. Multitouch should be a transparent addition, available where needed, not required where not supported. So we do pointer emulation for multitouch events, and it's actually specified in the protocol how we do it. Mainly so it's reliable and predictable for clients."
This second blog post covers pointer emulation on direct-touch devices, depenedent-touch devices, and button events and button state. Again, if you're really into input handling or working on multi-touch support for a tool-kit or an advanced application it's a worthwhile read, but otherwise it's not exactly a fun read.