System and private libraries can contain both procedures and INCLUDE groups. The order in which the system searches system and private libraries for INCLUDE groups is the same as the search order used for procedures (see "Using a Procedure" in topic 5.1.3).
INCLUDE groups cannot contain the following JCL statements:
PROC and PEND statements
JES2 and JES3 statements and commands
DD * and DD DATA statements
Do not define procedures in an INCLUDE group. However, you can put EXEC statements that invoke procedures in an INCLUDE group.