function popup(url) {// syntax: popup(url [, windowname [, width [, height [, window_top [, window_left]]]]])
	var int_screen_w, int_screen_h, int_window_w, int_window_h;

//	int_window_w = 300; // default window width
//	int_window_h = 300;
	int_screen_w = screen.availWidth; // available screen width
	int_screen_h = screen.availHeight;

	str_win_name = (arguments[1])? arguments[1] : " ";

	int_window_w = (arguments[2] > 100)? arguments[2] : int_screen_w; // window width = 300 if not supplied
	int_window_h = (arguments[3] > 100)? arguments[3] : int_screen_h; // window height = 300 if not supplied
	int_win_top  = ((arguments[4] > 0)&&(arguments[4] < int_screen_h))? arguments[4] : 0; // window top = 0 if not supplied
	int_win_left = ((arguments[5] > 0)&&(arguments[5] < int_screen_w))? arguments[5] : 0; // window left = 0 if not supplied
	scroll_bars  = (arguments[6] == 0)?  0 : 1;

	win = window.open(url, str_win_name,'width='+int_window_w+',height='+int_window_h+',screenx='+int_win_left+',scrollbars='+scroll_bars+',screeny='+int_win_top);
	win.moveTo(int_win_top,int_win_left);
	win.focus();
}

function checkForm(form){
	var str_error = "";
	switch (form.name){
		case "frm_aanmelden":
			str_error += (isValidEmailAddress(form.email.value))? "" : "Voer een geldig email adres in aub.\n";
			str_error += (form.passw1.value == "")? "Voer uw wachtwoord in aub.\n" : "";
			str_error += (form.passw1.value != form.passw2.value)? "Uw wachtwoord en wachtwoordbevestiging komen niet overeen.\n" : "";
			str_error += (form.akkord[0].checked)? "" : "U moet de algemene voorwaarden nog accepteren.\n";
			
			break;
		
		case "frm_inloggen":
			str_error += (isValidEmailAddress(form.email.value))? "" : "Voer een geldig email adres in aub.\n";
			str_error += (form.passw.value == "")? "Voer uw wachtwoord in aub.\n" : "";
			
			break;
			
		case "frm_verify_email":
			str_error += (form.code.value.length != 10)? "Voer een geldige bevestigingscode in aub.\n" : "";
			
			break;
					
		case "frm_edit_numbers":
			str_error += ( (form.phone.value.length != 10) || (! isNumeric( form.phone.value.length ) ) )? "Voer een geldig ( tien cijferig ) telefoon nummer in aub. Zonder spaties of streepjes (bv. 0612345678).\n" : "";
			str_error += ( (form.old_phone.value) && (form.phone.value ==  form.old_phone.value) )? "Het nummer is niet aangepast." : "";
			break;
			
		case "frm_reset_pass":
			str_error += (isValidEmailAddress(form.email.value))? "" : "Voer een geldig email adres in aub.\n";
			
			break;
			
		default:
			return false;
	}
	if (str_error == ""){ return true }
	else {
		alert(str_error);
		return false;
	}
}
// check to see if input is a valid email address
function isValidEmailAddress( val ) {
	var filter = /^[A-Za-z0-9_.-]*@[A-Za-z0-9_.-]+\.[A-Za-z0-9_.]+[A-za-z]$/;
	return ( filter.test(val) );
}
//
function confirmDelete(item) {
	if ( !confirm( "Weet u zeker dat u '"+item+"' wilt verwijderen?   " ) ) return false;
}
function isNumeric( val ) {
	var filter = /\D/;
	return !( filter.test(val) );
}