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+CONCEPT
+        uids (userids)
+
+DESCRIPTION
+        Every object in the mud is attributed with a user-id 'uid': a string
+        which associates the object with a certain 'user' (aka 'wizard' or
+        'creator', though it is not limited to that). The uid can be 0, which
+        internally is the default-uid.
+
+        The uid serves a dual purpose: on the on hand it is used to gather
+        statistics about the various groups of objects (in the famous
+        'wizlist'), on the other hand the uid can come in handy in the
+        implementation of security systems.
+
+        The uid of an object is assigned at its creation through the
+        driver hooks H_LOAD_UIDS for loaded objects, and H_CLONE_UIDS
+        for cloned objects, and can't be changed afterwards.
+
+        The uid of an object can be queried with the efun getuid() (resp.
+        creator() in compat-mode).
+
+
+        Every object also has a second string attribute, the 'effective
+        userid' or 'euid', which also may be 0. This value was intended to
+        implement a security system based on difference between theoretical
+        and effective permissions. Since the effectiveness of this system is
+        doubtful, the driver enforces such a use only as an option.
+
+        As uids, euids are assigned at an objects creation through
+        the two aformentioned driverhooks. They can be queried with
+        the efun geteuid() and changed with the efun seteuid(). Calls
+        to the latter are verified by the master lfun valid_seteuid().
+
+        Additionally objects can impose their uid onto an other objects
+        euid with the efun export_uid().
+
+
+        If the driver is run in 'strict euids' mode, euids are taken
+        more seriously than being just another attribute:
+          - all objects must have a non-0 uid.
+          - objects with a 0 euid can't load or clone other objects.
+          - the backbone uid as returned by master::get_bb_uid() must
+            not be 0.
+
+
+        Userids are assigned at the time of the creation of an object
+        by calling the driverhooks H_LOAD_UIDS and H_CLONE_UIDS:
+
+            mixed <load_uids closure> (string objectname)
+            mixed <clone_uids closure>(object blueprint, string objectname)
+
+        When an object is newly loaded, the H_LOAD_UIDS hook is
+        called with the object name as argument.
+        When an object is cloned, the H_CLONE_UIDS hook is called
+        with the blueprint object as first and the clone's designated
+        name as second argument.
+        In both cases the new object already exists, but has 0 uids.
+
+        For the result, the following possibilities exist (<num> is
+        a non-zero number, <no-string> is anything but a string):
+
+             "<uid>"                    -> uid = "<uid>", euid = "<uid>"
+             ({ "<uid>", "<euid>" })    -> uid = "<uid>", euid = "<euid>"
+             ({ "<uid>", <no-string> }) -> uid = "<uid>", euid = 0
+
+        If strict-euids is not active, the following results are
+        possible, too:
+
+             <num>                      -> uid = 'default', euid = 0
+             ({ <num>, "<euid>" })      -> uid = 'default', euid = "<euid>"
+             ({ <num>, <no-string> })   -> uid = 'default', euid = 0
+
+
+
+        Slightly different rules apply to the (e)uid of the master.
+        The masters (e)uid is determined by a call to
+        master->get_master_uid():
+
+             "<uid"> -> uid = "<uid>", euid = "<uid>"
+
+        In non-strict-euids mode, more results are possible:
+
+             0       -> uid = 0, euid = 0
+             <num>   -> uid = 'default', euid = 0
+
+        If your uids are in general based on filenames, it is wise to return a
+        value here which can not be legally generated from any filename.  OSB
+        for example uses 'ze/us'.
+
+        The masters uid is determined only on startup this way, at runtime the
+        uids of a reloaded master determined as for every object by a call to
+        the appropriate driver hooks.
+
+SEE ALSO
+        native(C), get_root_uid(M), valid_seteuid(M),
+        objects(C), clone_object(E), geteuid(E), getuid(E), seteuid(E)