function checkEnter(e) {
	var characterCode;
	if (e && e.which) {
		e = e;
		characterCode = e.which;
	}
	
	if (characterCode == 13) {
		checkForm(MyForm);
		return false;
	} else {
		return true;
	}
}

function checkForm(MyForm) {
	for (i = 0; i < MyForm.elements.length; i++) {
		if (MyForm.elements[i].value == "") {
			if (MyForm.elements[i].id.slice(-3) != "_nc") {
				alert("Niet alle elementen zijn ingevuld.");
				MyForm.elements[i].focus();
				return false;
			}
		}
	}
	MyForm.submit();
}