function CheckZip(object_value) {
    if (object_value.length == 0)
        return true;
    if (object_value.length != 5 && object_value.length != 10)
        return false;
	// make sure first 5 digits are a valid integer
	if (object_value.charAt(0) == "-" || object_value.charAt(0) == "+")
        return false;
	if (!CheckInteger(object_value.substring(0,5)))
		return false;
	if (object_value.length == 5)
		return true;
	// check if separator is either a'-' or ' '
	if (object_value.charAt(5) != "-" && object_value.charAt(5) != " ")
        return false;
	// check if last 4 digits are a valid integer
	if (object_value.charAt(6) == "-" || object_value.charAt(6) == "+")
        return false;
	return (CheckInteger(object_value.substring(6,10)));
}

function CheckInteger(object_value) {
    //Returns true if value is a number or is NULL
    //otherwise returns false	
    if (object_value.length == 0)
        return true;
    //Returns true if value is an integer defined as
    //   having an optional leading + or -.
    //   otherwise containing only the characters 0-9.
	var decimal_format = ".";
	var check_char;
    //The first character can be + -  blank or a digit.
	check_char = object_value.indexOf(decimal_format)
    //Was it a decimal?
    if (check_char < 1)
	return CheckNumber(object_value);
    else
	return false;
}

function CheckNumber(object_value) {
    //Returns true if value is a number or is NULL
    //otherwise returns false	

    if (object_value.length == 0)
        return true;

    //Returns true if value is a number defined as
    //   having an optional leading + or -.
    //   having at most 1 decimal point.
    //   otherwise containing only the characters 0-9.
	var start_format = " .+-0123456789";
	var number_format = " .0123456789";
	var check_char;
	var decimal = false;
	var trailing_blank = false;
	var digits = false;

    //The first character can be + - .  blank or a digit.
	check_char = start_format.indexOf(object_value.charAt(0))
    //Was it a decimal?
	if (check_char == 1)
	    decimal = true;
	else if (check_char < 1)
		return false;
        
	//Remaining characters can be only . or a digit, but only one decimal.
	for (var i = 1; i < object_value.length; i++)
	{
		check_char = number_format.indexOf(object_value.charAt(i))
		if (check_char < 0)
			return false;
		else if (check_char == 1)
		{
			if (decimal)		// Second decimal.
				return false;
			else
				decimal = true;
		}
		else if (check_char == 0)
		{
			if (decimal || digits)	
				trailing_blank = true;
        // ignore leading blanks

		}
	        else if (trailing_blank)
			return false;
		else
			digits = true;
	}	
    //All tests passed, so...
    return true
}