function tabnav(t){
	document.getElementById('waarom').style.display="none";
	document.getElementById('wat').style.display="none";
	document.getElementById('aspecten').style.display="none";

	document.getElementById('lwaarom').style.background="none";
	document.getElementById('lwat').style.background="none";
	document.getElementById('laspecten').style.background="none";

	if (t == 'waarom'){
	    document.getElementById('waarom').style.display="";
	    document.getElementById('lwaarom').style.background="#fff";
	}
	if (t == 'wat'){
	    document.getElementById('wat').style.display="";
	    document.getElementById('lwat').style.background="#fff";
	}
	if (t == 'aspecten'){
	    document.getElementById('aspecten').style.display="";
	    document.getElementById('laspecten').style.background="#fff";
	}
}