function blind_toggle_optionfield() {
    new Effect.toggle(
        'searchform-ui_options',
        'blind',
        {
            duration:0.5,
            afterFinish:update_label()
        }
    );
        
    return false;
}

function update_label() {
   var label_element = $("option_field_control");
   var hide_element  = $("searchform-ui_options");
   var keep_element  = $("keep_optionfield");
   
   if (hide_element.visible()) {
     label_element.innerHTML = '▼検索設定';
   } else {
     label_element.innerHTML = '▲検索設定';
   }
}