Self-multiplexing means the generation of multiple possible ways for reality to evolve, within reality itself. When one of these possibilities is chosen to be actualized, that is called self-selection.
The universe contains many objects but all of those objects have the universe from which they originate in common. The universe enforces some general rules on all of the objects within it as it topologically (physically) contains them. But it can also be said that the objects in the universe contain the universe because without all of the objects and their specific event histories/interactions, there would be no specific description of the universe to speak of. So the universe topologically contains its objects, which descriptively contain the universe.
Self Multiplexing refers to the universe creating objects out of itself to give it a specific description, however this is a specificity that is emerging still within the constraints of a global syntactic medium.