+The pap_logout_hook is called when the link is terminated, instead of
+pppd's internal `plogout' function. It can be used for accounting
+purposes. This hook is deprecated and will be replaced by a notifier.
+
+
+int (*null_auth_hook)(struct wordlist **paddrs,
+ struct wordlist **popts);
+
+This hook allows a plugin to determine what the policy should be if
+the peer refuses to authenticate when it is requested to. If the
+return value is 0, the link will be terminated; if it is 1, the
+connection is allowed to proceed, and in this case *paddrs and *popts
+can be set as for pap_auth_hook, to specify what IP addresses are
+permitted and any extra options to be applied. If the return value is
+-1, pppd will look in the pap-secrets file as usual.
+
+
+void (*ip_choose_hook)(u_int32_t *addrp);
+
+This hook is called at the beginning of IPCP negotiation. It gives a
+plugin the opportunity to set the IP address for the peer; the address
+should be stored in *addrp. If nothing is stored in *addrp, pppd will
+determine the peer's address in the usual manner.
+
+
+A plugin registers itself with a notifier by declaring a procedure of
+the form:
+
+void my_notify_proc(void *opaque, int arg);
+
+and then registering the procedure with the appropriate notifier with
+a call of the form
+
+ add_notifier(&interesting_notifier, my_notify_proc, opaque);
+
+The `opaque' parameter in the add_notifier call will be passed to
+my_notify_proc every time it is called. The `arg' parameter to
+my_notify_proc depends on the notifier.
+
+A notify procedure can be removed from the list for a notifier with a
+call of the form
+
+ remove_notifier(&interesting_notifier, my_notify_proc, opaque);
+
+Here is a list of the currently-implemented notifiers in pppd.
+
+* pidchange. This notifier is called in the parent when pppd has
+ forked and the child is continuing pppd's processing, i.e. when pppd
+ detaches from its controlling terminal. The argument is the pid of
+ the child.
+
+* phasechange. This is called when pppd moves from one phase of
+ operation to another. The argument is the new phase number.
+
+* exitnotify. This is called just before pppd exits. The argument is
+ the status with which pppd will exit (i.e. the argument to exit()).
+
+* sigreceived. This is called when a signal is received, from within
+ the signal handler. The argument is the signal number.
+
+* ip_up_notifier. This is called when IPCP has come up.
+
+* ip_down_notifier. This is called when IPCP goes down.
+
+* auth_up_notifier. This is called when the peer has successfully
+ authenticated itself.
+
+* link_down_notifier. This is called when the link goes down.
+
+