One piece of advice I often see given to new writers is to keep your POV locked to one character. Yet in published works, I see this 'rule' broken all the time. One explanation I've heard is that it used to be ok but now it's not. But I guess I struggle with the rationale behind that. If it works it works, right? So would an editor reject a story just because of a POV shift? Or if not a shift, but POV that is able to show things that the central character would not be able to see? How does one employ dramatic irony then, or is that a taboo now as well?