Restrictions and Limitations of an IPCS Exit Routine

For IPCS and ABEND/SNAP Formatting
An exit routine can use system services that cause TCBs and service request blocks (SRB) other than the original TCB to perform processing. Such TCBs and SRBs cannot request dump-processing services.

Entry to exit routines must be in primary mode, and all services invoked by the exit routine expect to receive control in primary mode. In between, however, an exit routine may switch to AR mode for any processing that might require AR mode.
For IPCS Formatting
Exit routines should be reentrant and recursively enterable. Existing verb exit routines that do not satisfy this criterion can be used with the restriction that the IPCS dialog user cannot call for their recursive use. In this case, the verb exit routines should be marked with neither the RENT nor the REUS linkage editor attributes so that the user of the IPCS dialog can cause multiple, independent copies of the exit routine to be loaded and run under each ISPF logical screen task.
When using any of the IPCS print services, follow these guidelines to design messages issued by IPCS:
1. Do not use EBCDIC codes that cannot be represented on all the media to which IPCS messages may be transmitted. Lowercase EBCDIC letters may be treated as an exception to this rule because IPCS will translate lowercase letters to uppercase if the user requests.
2. IPCS limits the EBCDIC codes that you may use by translating all unprintable codes to EBCDIC periods. IBM® does not recommend that you use richer fonts than the CHARS=DUMP font, but IPCS does not prevent you from using these fonts.
  Reference
  
  See z/OS MVS IPCS User's Guide for information about how IPCS treats different print fonts.
3. Do not design reports in which lines of text refer to other parts of the report through page numbers. For reports that are quite extensive, consider using the table of contents service to help the report user find the parts of the report that are of interest. The table of contents service allows the report user to:
  - Supply a data set specifically for the table of contents information
  - Direct the IPCS print output to another data set where IPCS can include page headers that include the referenced page numbers.
  If the report user decides not to use the table of contents entries, IPCS discards them.
  
  When a report is written to a terminal instead of a print data set, no page headers (and, therefore, no page numbers) are displayed. Thus, references to page numbers are of limited value in a report written to a terminal; the page number references merely provide some indication of the relative locations of various items in a report.
For ABEND/SNAP Formatting
An exit routine should not alter the environment being dumped. Resources that are allocated for processing by an the routine should be returned to their original state before the routine ends processing.