The DOM selection corresponds to the primary selection, the others are drawn using CSS spans. This means you only get touchscreen-style handles on the primary one, but I think that's acceptable.
By the way, how do we select multiple lines in chrome? I can do it in firefox in the "old" CodeMirror, but not in my chromebook.
Mouse drag or shift up/down works for me? Or what kind of selecting are you trying to do? (Or, if this was about multiple _cursors_, those are only half-implemented, and not exposed through the UI yet.)