Code
<span onkeydown="apoLeng()" onfocus="apoLeng();">$FLD_MESSAGE$</span>
<script>
// Оставшееся количество символов в чате by Csomsk.Ru
function apoLeng() {
var a = $('#mchatMsgF').val();
if(a.length == 100-1) {var hm = 400;apoT()} else if(a.length == 200-1) {var hm = 300;apoT()} else if(a.length == 300-1) {var hm = 200;apoT()} else if(a.length == 400-1) {var hm = 100;apoT()} else if(a.length == 450-1) {var hm = 50;apoT()} else if(a.length == 500-1) {var hm = 0;apoT()};
function apoT() {
_uWnd.alert('Осталось '+hm+' символов', '', {w:200, h:70, name:'aPoln'})}};
</script>