Once a superhero franchise goes multiverse, it’s hard to go back.

No work of fiction ever needs permission to break the rules or push the boundaries of traditional storytelling, but the multiverse, at least as it’s been served up in recent Marvel movies, practically demands it. And for the moment that means a lot of cameo opportunities. “ Spider-Man: No Way Home ” opened the door to the concept, to mostly charming results, but now Benedict Cumberbatch’s master of the mystic arts is flying through the interdimensional portal with the concept in “ Doctor Strange in the Multiverse of Madness.”

This film is technically the sequel to “Doctor Strange,” a movie that came out six years ago. But so much has happened in Marvel land that involves Stephen Strange and his goatee — “Infinity War,” “Endgame” and, yes, the most recent “Spider-Man” — that where it falls in the “Doctor Strange” standalone film continuity is entirely beside the point. One could not simply watch “Doctor Strange” and then “Doctor Strange 2” and expect it to make sense.