function isDate(dateStr) 
{
    var datePat = /^(\d{1,2})(\/|-)(\d{1,2})(\/|-)(\d{4})$/;
    var matchArray = dateStr.match(datePat); // is the format ok?

    if (matchArray == null) 
    {
        alert("Please enter your date as dd/mm/yyyy. Your current selection reads: " + dateStr);
        return false;
    }

    day = matchArray[1]; // p@rse date into variables
    month = matchArray[3];
    year = matchArray[5];

    if (month < 1 || month > 12) 
    { // check month range
        alert("Month must be between 1 and 12.");
        return false;
    }

    if (day < 1 || day > 31) 
    {
        alert("Day must be between 1 and 31.");
        return false;
    }

    if ((month==4 || month==6 || month==9 || month==11) && day==31) 
    {
        alert("Month "+month+" doesn't have 31 days!");
        return false;
    }

    if (month == 2) 
    { // check for february 29th
        var isleap = (year % 4 == 0 && (year % 100 != 0 || year % 400 == 0));
        if (day > 29 || (day==29 && !isleap)) 
        {
            alert("February " + year + " doesn't have " + day + " days!");
            return false;
        }
    }
    return true; // date is valid
}