function cartCheckZip() {
	var oForm = document.forms["cartUpdateForm"];
	var oDestInput = oForm.elements["service_destination"];
	var oInput = oForm.elements["dom_zip"];
	
	var sValue = new String(oInput.value);
	var sPattern = /^\d{5}(-\d{4})?$/;
	
	if ( ! oDestInput[0].checked ) return true; // not a domestic order
	
	if ( sValue.search(sPattern) == -1 ) {
		alert("The zip code " + sValue + " is invalid. Please enter a zip code in the form of 12345 or 12345-1234");
		oInput.value = "";
		oInput.focus();
		return false;
	}
	
	return true;
}