treehead

    OpenVMS usage:address
    type:         address
    access:       read only
    mechanism:    by reference

    Tree head of the binary tree. The treehead argument is the
    address of an unsigned longword that is the tree head in the
    binary tree traversal.

 user-action-procedure

    OpenVMS usage:procedure
    type:         procedure value
    access:       function call (before return)
    mechanism:    by value

    User-supplied action routine called by LIB$TRAVERSE_TREE for each
    node in the tree. The user-action-procedure argument must return
    a success status for LIB$TRAVERSE_TREE to continue traversal.

 user-data-address

    OpenVMS usage:user_arg
    type:         longword (unsigned)
    access:       read only
    mechanism:    by reference

    User data that LIB$TRAVERSE_TREE passes to your action routine.
    The user-data-address argument contains the address of this user
    data. This is an optional argument; the default value is 0.