From musical festival violence to the pen pal bond between Johnny Cash and Bob Dylan, Mangold tells us what's real and what's not in "A Complete Unknown."

How does it feel?” is one way by which to measure a movie. But if you’ve seen “A Complete Unknown,” the Bob Dylan biopic that opened on Christmas Day, you may have left the theater singing to yourself (to the tune of “Like a Rolling Stone”): How much is reeeaaallll?