function toggle(velda){
	veld1='item'+velda;
	veld2='img'+velda;
	
	if(document.getElementById(veld1)){
		if(document.getElementById(veld1).style.display  == 'none'){
			document.getElementById(veld1).style.display = '';
			document.getElementById(veld2).src = 'http://www.duikschool.nu/site/image/icon/min_folder.png';
			document.getElementById(veld2).alt = '-';
			
		} else {
			document.getElementById(veld1).style.display = 'none';
			document.getElementById(veld2).src = 'http://www.duikschool.nu/site/image/icon/plus_folder.png';
			document.getElementById(veld2).alt = '+';
		}
	}
}