function vld(sender, result)
{
    if( result) // valid
    {
        sender.className = sender.className.replace( "invalid", "");
        return true;
    }
    else    // invalid
    {
        if( sender.className.indexOf("invalid") == -1)
            sender.className += " invalid";
        return false;
    }
}

function vldNotEqual(sender, exp)
{
    return vld(sender, sender.value != exp);
}

function vldNotEqual(sender, exp1, exp2)
{
    return vld(sender, sender.value != exp1 && sender.value != exp2);
}

function vldEqual(sender, exp)
{
    return vld(sender, sender.value == exp);
}

function vldGreater(sender, exp)
{
    return vld(sender, sender.value > exp);
}

function vldGreaterEqual(sender, exp)
{
    return vld(sender, sender.value >= exp);
}

function vldSmaller(sender, exp)
{
    return vld(sender, sender.value < exp);
}

function vldSmallerEqual(sender, exp)
{
    return vld(sender, sender.value <= exp);
}

function vldLengthEqual(sender, exp)
{
    return vld(sender, sender.value.length == exp);
}

function isValid(sender)
{
    return sender.className.indexOf("invalid") == -1;
}