Running a started task under a job entry subsystem

These additional considerations apply to a started task running under a job entry subsystem (JES):

The JCL for the started task may contain commands and JES2 JECL statements. It may not use JES3 JECL.
In JES3, the JCL may contain a JCLLIB statement, and the started task may have a SYSIN data set, but these are permitted only if the JCL being started is a complete job. For example, the following will work in JES3:
```
   //STC    JOB
   //       JCLLIB ORDER=...
   //STEP1  EXEC   PGM=...
   //MYDATA DD     *
   These are the times that try men's souls.
   /*
   //
```

In JES2, the JCL may contain a JCLLIB statement, and the started task may have a SYSIN data set. For example, the following will work in JES2:

//HELLO     PROC
//STEPA     EXEC  PGM=IEBGENER
//SYSIN     DD    DUMMY
//SYSPRINT  DD    SYSOUT=A
//SYSUT2    DD    SYSOUT=A
//SYSUT1    DD    DATA
HELLO WORLD
/*
//          PEND

The started task may have SYSOUT data sets.
JES exits get control (to validate and modify the task).