var agent=navigator.userAgent.toLowerCase();
var ie = ((agent.indexOf("msie") != -1)&&(agent.indexOf("opera")==-1));

function updateBirthdayFields()
{
    var yearListObject = document.getElementById('birth_year');
    var year = yearListObject.options[yearListObject.selectedIndex].value;
    if (!year) {
        return;
    }
    var monthListObject = document.getElementById('birth_month');
    var month = monthListObject.options[monthListObject.selectedIndex].value;
    if (!month) {
        return;
    }
    var dayListObject = document.getElementById('birth_day');
    var day = dayListObject.options[dayListObject.selectedIndex].value;
    var dayList = new Array(31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31);
    dayList[1] = (((year % 4) == 0) && ((year % 100) != 0) || ((year % 400) == 0)) ? 29 : 28;
    var lastMonthDay = dayList[month - 1];
    if (day > lastMonthDay) {
        dayListObject.selectedIndex = lastMonthDay;
    }
}