diff --git a/doc/hook/clean_up b/doc/hook/clean_up
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+SYNOPSIS
+        #include <sys/driver_hooks.h>
+
+        set_driver_hook(H_CLEAN_UP, value)
+
+        <value> being:
+
+          int <closure>(int ref, object ob)
+          void|int <name>(int ref)
+
+DESCRIPTION
+        Optional hook to clean up an object.
+        Hook setting can be any closure, or the name of the function
+        to call in the object.
+
+        This hook is called for an object if it hasn't been used
+        for at least TIME_TO_CLEAN_UP seconds, to give it the
+        opportunity to self destruct.
+
+        If the hook is a closure, it is called with the refcount of
+        the object to clean up as first argument, and with the object
+        itself as second. Lambda closures are also bound to the object
+        prior to the call.
+
+        If the hook is the name of an lfun, it is called in the
+        object with its refcount as argument.
+
+        In both calls, the refcount is constructed as:
+
+          ref = 0: the object is a clone, or a blueprint with
+                   replaced program.
+          ref = 1: the object is a swapped or unused blueprint.
+          ref > 1: the object is a used blueprint with <ref> references.
+
+        The cleanup method has the possibility to destruct the
+        object. To survive this time, but try again some time later,
+        the call has to result in a non-zero value.
+
+        If the hook specifies a non-existing lfun, or if the call
+        returns 0, no further attempt to clean up this object will be done.
+
+HISTORY
+
+SEE ALSO
+        hooks(C)