Next is a snippet from the announcement:

" Following some discussions with Juha regarding some extension for the branch flags, we decided it is better to have a re-design of flags in openser to allow a better flexibility and extensibility without any consistency penalties.

What we had so far:
   - message flags (or transaction flags) which are transaction persistent
   - pseudo-branch flags - a set of flags from the message flags were handled by TM as branch flags
          (saved per branch and not only per transaction).

What we have now:
   - message flags (or transaction flags) will works as they do now, but the branch mask will be removed (rolling back as in 0.9.x versions). These flags are transaction persistent.
   - branch flags (NEW) are saved also in transaction, but per branch; also they will be saved in usrloc (per contact). A new set of functions were added for manipulating these flags from script. So, there flags will be registration persistent and branch persistent.
   - script flags (NEW) are no-message-related flags - they are only script persistent and you can strictly use them for scripting. Once you exit a top level route, they will be lost. These flags are useful and they offer an option to de-congest the message flags - many flags have no need to be saved as they just reflect some scripting status. "

See full announcement:

http://openser.org/pipermail/devel/2007-January/005228.html