I think it's better understood as, "global and static state should only be declared by the client". So all of your functions should take pointers and all of you

I think it's better understood as, "global and static state should only be declared by the client". So all of your functions should take pointers and all of your data should preferably be declared as types, and the points of your program that consume your code can declare their lifetime. So if you're inclined to declare 2 global variables, instead define a struct with those two values and your functions take a pointer to that struct, and whatever code calls into yours can then decide whether they want to define that struct as having global scope. It just makes for more modular code.