It is encapsulation with the mandatory law stating that an encapsulation of an encapsulation must be as deep as a single encapsulation.

Note that this informal statement doesn't necessarily mean you have to be encapsulating data. A behavior, a contract, an assertion, compositions of all of these etc can also be encapsulated.

Fun ideas (not necessarily true but fun to think about):

* Monads kinda convert nesting to concatenations.

* A monad is the leakiest of the abstractions. You are always a single level of indirection away from the deepest entity encapsulated within.

* What's common among brackets, curly braces and paranthesises(?) is them being monadic if you remove them from their final construction while keeping the commas or semicolons.

Very important note: You should have already stopped reading by now if you got angry to due these false analogies.