When you are using STEPLIB to test new maintenance or a new release 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). For more information, refer to the z/OS ISPF Dialog Developer's Guide and Reference.

If you are using the ISPF client/server (ISPF C/S) feature or the z/OS® UNIX Table Utility, the Language Environment® run-time library data sets SCEERUN and SCEERUN2 must be in STEPLIB or LNKLST. The modules in these data sets are not searched for in ISPLLIB.