Joanna Newsom creates small, bustling universes within her songs, which take on the form of fairy tales, medieval allegories or meditations on war, time and mortality. It’s tempting, then, to treat them like works of fiction, to follow along with a lyrics sheet in order to keep up with the fables she’s relaying. But the singer, songwriter and harpist, who performs at the Bing Crosby Theater next week, says she’s more concerned with mood, tone and atmosphere than the actual lyrical content.