I became intrigued with where UML 2.x has gotten to and have been looking for a good concise description of the new syntax but this appears harder to find than you would think.  To me OMG does itself a disservice by not putting something together for this end.  UML is heavily criticized for being overly complex and a good part of this is in how it is described.

Wikipedia did lead me to this link which I really liked http://www.holub.com/goodies/uml/ Hopefully the author will continue to extend his work.