Why "return 0;"

[compsystems]

Why the template of a new function in CAS mode, the declaration "RETURN 0" returns the number zero?

I think the logical thing is to return 1 (true or done), synonymous that the function reached the goal, while that 0 is synonymous with false.

PHP Code:

#cas
    functionName():=
    BEGIN
       return 0;
    END;
#end