function chkForm() {
    
	if(document.forms['nieuwsbriefform'].elements['email'].value == '' || document.forms['nieuwsbriefform'].elements['email'].value == 'uwnaam@provider.nl') {
		alert('Vul a.u.b. uw e-mailadres in');
		document.forms['nieuwsbriefform'].elements['email'].focus();
		return false;		
	}
	
	var veldinhoud = document.forms['nieuwsbriefform'].elements['email'].value;
	var patroon = "^([a-zA-Z0-9]){1,}(([a-zA-Z0-9\-_])|(([\.]){1,1}([a-zA-Z0-9]){1,})){0,}([@]){1,1}([a-zA-Z0-9]){1,}(([a-zA-Z0-9\-_])|(([\.]){1,1}([a-zA-Z0-9]){1,})){0,}([\.]){1,1}([a-zA-Z0-9]){2,4}$";
	var match = new RegExp(patroon);

	if(!match.test(veldinhoud)) {
		alert('Het e-mailadres is ongeldig.');
		document.forms['nieuwsbriefform'].elements['email'].focus();
		return false;
	}

}