function toggleCheckboxes(field_id) {
	//determine which group the checkbox is in via the id
        var el = document.forms['adv_search'][field_id];

	var underscore=el.id.indexOf('_');
	var group=el.id.substring(0,underscore);
	
	//if checked all, uncheck individuals and visa versa
	if (el.id.indexOf(group + '_all')!=-1 && el.checked==true) {
		var individualChoice=document.getElementById(group + '_choices_container').getElementsByTagName('*');
			for (var i6=0; i6<individualChoice.length; i6++) {
				if (individualChoice[i6].type=="checkbox") {
					individualChoice[i6].checked=false;
				}
			}
	}else{
		document.getElementById(group + '_all').checked=false;
	}
		
}