DFHUERTR (the function definition)

The function definition identifies the caller of the task-related user exit program. The DSECT contains two symbolic definitions (fields).
UERTFGP
A single byte that is set to X'00'. The zero setting shows that this is a task-related user exit invocation and that the parameter list therefore includes the fields UEPTAA, UEPTAL, UEPEIB, UEPURID, and UEPFLAGS.
UERTFID
A single-byte identifier that shows whether this call has been made by an application program, the CICS® SPI manager, the CICS syncpoint manager, the CICS task manager, the CICS termination manager, CICS context management, CICS application environment management, or by EDF. It can have one of the following seven settings:
UERTSPI
(X'01') CICS SPI call.
UERTAPPL
(X'02') Application program call.
UERTSYNC
(X'04') CICS syncpoint manager call.
UERTTASK
(X'08') CICS task manager call.
UERTCTER
(X'0A') CICS termination call.
UERTFEDF
(X'0C') EDF call.
UERTSWAE
(X'OD') Switch application environment call.
UERTFCON
(X'0E') CICS context management call.

It is important to know which type of program has made the call because it affects how the calling program’s parameter list is interpreted by the task-related user exit program.