The DEFINE COLLECTION command creates a collection. A collection
    allows you to view and manipulate a group of related elements
    that make up a particular system or subsystem.

    Because a collection is a controlled element, you use the DEFINE
    COLLECTION command to create the initial version of a collection.
    Use the RESERVE and REPLACE commands to create new versions.

    Before you issue the DEFINE COLLECTION command, you must create
    and set a context. The SHOW CONTEXT command indicates whether you
    have completed these steps.

    Because all elements in a collection hierarchy are children
    of the top collection, you can issue commands that affect the
    entire hierarchy with the /DESCENDANTS or /CLOSURE qualifiers.
    Because most elements in a collection hierarchy are also children
    of smaller subcollections beneath the top collection, you can
    also issue commands that affect only one subcollection and its
    children.

    To create a collection hierarchy, issue the DEFINE COLLECTION
    command immediately after the SET CONTEXT command. SET CONTEXT
    implicitly sets the collection you define as the top collection
    in the hierarchy, provided that you did not set a top collection
    within the DEFINE CONTEXT command.

    To extend the hierarchy beneath the top collection, you issue the
    following commands:

    1. DEFINE COLLECTION to create the collections that participate
       in the hierarchy. This command attaches all collections in the
       first level beneath the top collection.

    2. DETACH FROM COMPOSITE to detach those collections destined for
       lower levels in the hierarchy from the first level beneath the
       top collection.

    3. RESERVE and ATTACH TO COMPOSITE to reserve collections in each
       successive level and attach their immediate children.

    4. REPLACE to store in a partition the elements you have created.