Typical User Defined Function
<?php
function log_data($user, &$data) {
 mysql_query("INSERT INTO userdata VALUES ('".
            uniqid()."', '$user', '$data')");
}
?>
Pass-by-reference
<?php log_data($PHP_AUTH_USER, $data); ?>
Default values
<?php
function head($title="Default Title") {?>
    <HTML><HEAD><TITLE>
    <? echo $title ?>
    </TITLE></HEAD><BODY><?
}

head();
?>