//campo email
function emailvalidation(entered, alertbox) {
	with (entered) {
		apos=value.indexOf("@"); 
		dotpos=value.lastIndexOf(".");
		lastpos=value.length-1;
		if (apos<1 || dotpos-apos<2 || lastpos-dotpos>3 || lastpos-dotpos<2) {
			if (alertbox) {
			alert(alertbox);
			} 
			return false;
		}
		else {
		return true;
		}
	}
} 
//campo vuoto
function emptyvalidation(entered, alertbox) {
	with (entered) {
		if (value==null || value=="") {
			if (alertbox!="") {alert(alertbox);
		} 
			return false;
		}
		else {
			return true;
		}
	}
}