When you use ALTLIB under ISPF, you can pass the alternative library definitions from application to application by using ISPEXEC SELECT with the PASSLIB operand; for example:

ISPEXEC SELECT NEWAPPL(ABC) PASSLIB

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.