function numeralsOnly(evt) {
	evt = (evt) ? evt : event;
	var charCode = (evt.charCode) ? evt.charCode : ((evt.keyCode) ? evt.keyCode :
		((evt.which) ? evt.which : 0));
	if (charCode >31 && (charCode < 48 || charCode > 57)) {
		alert("Alleen nummers in dit veld a.u.b.");
		return false;	
	}	
	return true;
}

function blockEnter(evt) {
	evt = (evt) ? evt : event;
	var charCode = (evt.charCode) ? evt.charCode : ((evt.which) ? evt.which : evt.keyCode);
	if (charCode == 13 || charCode == 3) {
		return false;
	} else {
		return true;
	}
}

function toggle_visibility(id) {
	var e = document.getElementById(id);
   	if(e.style.display == 'block')
      	e.style.display = 'none';
   	else
      	e.style.display = 'block';
}

function popup(n,height,width)
{
	var window_height = height;
	var window_width = width;
	var screen_l = screen.width / 3;
	var screen_t = screen.height / 3;

	screen_l = (screen_l - (window_width / 3));
	screen_t = (screen_t - (window_height / 3)) - 10;

	welke = n;
	var options = 'width=' + window_width + ',height=' + window_height + ',left=' + screen_l + ',Top=' + screen_t + ',toolbar=0,menubar=0,location=0,scrollbars=1,directories=0,status=0,resizable=0'
	window.open( welke, 'popup' ,options ) ;
}