function validate_numbers(evt) {
    evt = (evt) ? evt : ((event) ? event : null);
    if (evt) {
        var charCode = (evt.charCode || evt.charCode == 0) ? evt.charCode : 
                       ((evt.keyCode) ? evt.keyCode : evt.which);
        if (charCode > 13 && (charCode < 48 || charCode > 57)) {
            //alert("Only whole numbers are allowed.");
            if (evt.returnValue) {
                evt.returnValue = false;
            } else if (evt.preventDefault) {
                evt.preventDefault();
            } else {
                /*return false;*/
				event.returnValue=false;
            }
        }
    }
}
function remove(){
	if (document.getElementById('conditions_msg').style.display='block'){
		document.getElementById('conditions_msg').style.display='none';
	} else {
		document.getElementById('conditions_msg').style.display='block';
	}
}

function check_firstname(){
	document.getElementById('label_firstname').innerHTML="Voorletters";
	document.getElementById('label_firstname').className="";
}
function check_lastname(){
	document.getElementById('label_lastname').innerHTML="Naam";
	document.getElementById('label_lastname').className="";
}
function check_street(){
	document.getElementById('label_street').innerHTML="Straat";
	document.getElementById('label_street').className="";
}
function check_number(){
	document.getElementById('label_number').innerHTML="Huisnummer";
	document.getElementById('label_number').className="";
}
function check_postcode(){
	document.getElementById('label_postcode').innerHTML="Postcode";
	document.getElementById('label_postcode').className="";
}
function check_city(){
	document.getElementById('label_city').innerHTML="Woonplaats";
	document.getElementById('label_city').className="";
}
function check_email(){
	document.getElementById('label_email').innerHTML="E-mail";
	document.getElementById('label_email').className="";
}
function check_quantity(){
	document.getElementById('label_quantity').innerHTML="Aantal boeken";
	document.getElementById('label_quantity').className="";
}
function check_comments(){
	document.getElementById('label_comments').innerHTML="Bericht";
	document.getElementById('label_comments').className="";
}
function check_conditions(){
	document.getElementById('label_conditions').innerHTML="<a href=\"?id=voorwaarden\" target=\"_blank\">Akkoord voorwaarden</a>";
	document.getElementById('label_conditions').className="";
}