REM, DIM, DECLARE, OPTION, and DATA statements are called declarative statements.
Declarative statements are valid only if they are just written.
Any declarative statement is processed on compiling, and is not an object of the control.
The following code let the lower bound of indices of B to be 0 even if the value of A is non-positive.
20 IF A>0 THEN 30 OPTION BASE 0 40 END IF 50 DIM B(10)
In addition, the scope of a declarative statement is the .program unit.