function CheckFieldFilled(elem)
{
    var ok = (elem.value != '');

    if (elem.id == 'mail')
    {
        if (!elem.value.match(/^([a-zA-Z0-9]|[a-zA-Z0-9]+[a-zA-Z0-9\._-]*[a-zA-Z0-9]+)@([a-zA-Z0-9]|[a-zA-Z0-9]+[a-zA-Z0-9\._-]*[a-zA-Z0-9]+)\.([a-zA-Z]{2,3})$/i))
        {
            ok = false;
        }
    }

    elem.className = (!ok)? 'required-input' : '';
}//CheckFieldFilled