6.3c

SYNTAX            : :L REG

RESULTING ARGUMENT: Size of the stack of the register (0 = no stack at all)
                    In array terms: the size of the array without counting entry [0].

FUNCTION          : Count the stack depth of a register. This is the amount
                    of pop commands that can be executed successfully.

EXAMPLE           : :L0 ^0 ESC
                    This command pops the entire stack for register 0,
                    discarding all previous content, regardless of how large the stack is.

MATRIX