CALL usersubname$ [,usersubparameters,..]
This is an efficient way of programmatically calling user defined subroutines.
In many cases it can allow you to get rid of complex SELECT and IF THEN ELSEIF ENDIF clauses and is processed in a much more efficient way.
The "usersubname$" can be any string or variable or function that resolves to the name of a normal user subroutine (not an in-built command). The "usersubparameters" are the same parameters that would be used to call the subroutine directly. A typical use could be writing any sort of emulator where one of a large number of subroutines should be called depending on some variable. It also allows a way of passing a subroutine name to another subroutine or function as a variable.
See also the CALL() function.