When using STEPLIB to test either new maintenance, releases, or versions of ISPF, and an ISPLLIB is allocated, those data sets allocated to STEPLIB that contain ISPF load modules should also be allocated to ISPLLIB. This prevents the possibility of mixed code (production code versus code to be tested).

The exceptions to this search order are the Language Environment® run-time library data sets SCEERUN and SCEERUN2. Modules in these data sets are not searched for using the ISPLLIB task library. SCEERUN and SCEERUN2 must be in STEPLIB or LNKLST if you are using the ISPF C/S feature or the z/OS® UNIX Directory List utility. See Language Environment considerations for more information about SCEERUN and SCEERUN2.

For more information about search order, refer to z/OS ISPF User's Guide Vol I.