-function subscribe_lists_event($participate, $uid, $evt, $paid, $payment = null)
+/** Subscribes user to various event related mailing lists.
+ *
+ * @param $uid: user's id.
+ * @param evt: events data, in particular ids of the lists at stake.
+ * @param participate: indicates if the user takes part at the event or not;
+ * -1 means he did not answer, 0 means no, and 1 means yes.
+ * @param paid: has the user already payed anything?
+ * 0 means no, a positive amount means yes.
+ * @param payment: is this function called from a payment page?
+ * If true, only payment related lists should be updated.
+ */
+function subscribe_lists_event($uid, $evt, $participate, $paid, $payment = false)