function checkall (sender, prefix) {
	var elements=document.getElementsByTagName("input");
	var objname = new String;
	for (i=0;i< elements.length;i++) {
		objname = elements[i].name;
		if (objname.substring(0, prefix.length)==prefix) {
    		if (sender.checked==true) {
    			elements[i].checked = true;
    		} else {
    			elements[i].checked = false;
    		}
    	}
	}
}