My observations (since beta, it might have changed):
  • Once target nametag becomes clickable (visible), it is appended into a list of targets for you
  • TAB will only target nearest if you have no target
  • If you have a target, TAB will target the "next in the list" according to the said list above
I was going to test it's relationship to the letter-designations but thought they'd "fix" this so never really tested it.