VMS Help RMS, XABPRO  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    The protection XAB (XABPRO) specifies the ownership,
    accessibility, and protection for a file. Although an application
    program typically uses a XABPRO as input to establish file
    protection when it creates a file, it can also use the XABPRO
    to change file protection when it closes a file. The program that
    opened the file can change file protection when it closes the
    file only if it accessed the file to make modifications and has
    control access.

    The following table lists the symbolic offset, the size in bytes,
    FDL equivalent, and a brief description of each field.

    Offset         FDL Equivalent    Description

    XAB$L_ACLBUF   None              Address of buffer that contains
                                     ACL
    XAB$L_ACLCTX   None              ACL positioning context
    XAB$W_ACLLEN   None              Receives the length of an
                                     ACL during an Open or Display
                                     service
    XAB$W_ACLSIZ   None              Length of buffer containing
                                     binary ACEs
    XAB$L_ACLSTS   None              System error status for ACL
                                     processing
    XAB$B_BLN      None              Block length
    XAB$B_COD      None              Type code
    XAB$W_GRP      FILE OWNER        Group number of file owner
    XAB$W_MBM      FILE OWNER        Member number of file owner
    XAB$B_MTACC    FILE MT_          Magnetic tape accessibility
                   PROTECTION
    XAB$L_NXT      None              Next XAB address
    XAB$W_PRO      FILE PROTECTION   File protection; contains
                                     four separate fields denoting
                                     protection for system, owner,
                                     group, and world
    XAB$B_PROT_    None              File protection options
    OPT
    XAB$L_UIC      FILE OWNER        User identification code;
                                     contains both the group and
                                     member fields