I guarantee this is a question that has been asked at this forum and the DW forums many times, but for the life of me I can't find an answer, so my apologies in advance.
In the exciting new Dungeon World rules (loaded up all snazzy on my Kindle, waiting for the hard copy in the mail, starting a new - hopefully ongoing - game next week, woot) the End of Session move says that characters mark XP when they resolve bonds, hit their alignment move and answer any of the three Big Questions. Perfectly clear!
But somewhere else in the text I caught a reference to marking XP when you roll 6 or less. I can't remember where I saw it, and I can't find any corroboration. Was I drunk? Or is that a rule?