Tanner (not his real name) sat in the stairwell connecting the first and second floors of a parking structure near the Santa Ana Civic Center on a recent, cold Saturday afternoon. His rib cage was visible through a snug, faded red T-shirt; his long, dark hair exaggerated the thirtysomething's jolty mannerisms. Snapping out of a trance, he glanced around, then grabbed something from a white paper bag between his legs. In one quick motion, Tanner rolled up his left sleeve, wrapped a rubber tourniquet around his upper bicep, then dropped his left arm to the cement. He cleaned off the soft, inner crease connecting his forearm and bicep with an antibacterial wipe before reaching back into the bag