When Open parameters is not selected, Open parmeters are disabled.

When Open parameters is selected, a variable declared using the string keyword is an open string parameter.

The actual parameter of an open string parameter can be a variable of any string type, and within the procedure or function, the size attribute (maximum length) of the formal parameter will be the same as that of the actual parameter.

Open string parameters behave exactly as variable parameters of a string type, except that they cannot be passed as regular variable parameters to other procedures and functions.

Open parameters is equivalent to {$P}.