A new version of the ULFM specification accounting for remarks and discussions going on at the MPI Forum Meetings in 2016 has been posted under the ULFM Specification item.
This new update has very few semantic changes. It clarifies the failure behavior of MPI_COMM_SPAWN, and corrects the output values of error codes and status objects returned from functions completing in error.
Head to ULFM Specification for more info.