Specifies the identifiers for the new or modified access
    privilege set entry. Specifying PUBLIC is equivalent to a
    wildcard specification of all user identifiers.

    In ANSI/ISO-style databases, you are allowed to specify only
    single-user user identifiers; no general or system identifiers
    are allowed. Access privilege set entries identify only those
    users who are common to all groups defined by the individual
    identifiers. Users who do not match all identifiers are not
    controlled by that entry. ANSI/ISO-style access privilege sets
    support only user identifiers.