Isolde is kind of wrong. The error handlers are stacked with set_error_handler(), and popped with restore_error_handler(). Here i put an example:
<?php
mysql_connect("inexistent"); function foo1() {echo "<br>Error foo1<br>";}
function foo2() {echo "<br>Error foo2<br>";}
function foo3() {echo "<br>Error foo3<br>";}
set_error_handler("foo1"); set_error_handler("foo2"); set_error_handler("foo3"); mysql_connect("inexistent");
restore_error_handler(); mysql_connect("inexistent");
restore_error_handler(); mysql_connect("inexistent");
restore_error_handler(); mysql_connect("inexistent");
restore_error_handler(); ?>