. Under ISPF, you can pass the alternative library definitions from application-to-application by using ISPEXEC SELECT with the PASSLIB operand. . The PASSLIB operand passes the ALTLIB definitions to the invoked application. . When the invoked application completes and the invoking application regains control, the ALTLIB definitions that were passed take effect again, regardless of whether the invoked application changed them. . If you omit the PASSLIB operand, ALTLIB definitions are not passed to the invoked application.