I resolve with this
//maxLen
{ type:function(ui){
var value = ui.value;
if(value.length > 50 ){
alert('some message');
return false;
}
}
}
but I have other question.
when I put return false, the entered value is cleared, then I comment the line //return false,the entered value remains in the cell but the alert is displayed 2 times,
how i can remain the entered value and return false?