code: public static String tooltip(Field field) {
          final String tooltip = field.getTooltip();
          if (tooltip == null) {
              return "";
          }
          return "<img class='tooltip' title='" + tooltip + "' alt='?' src='"
                  + getContextPath() + "/templates/"
                  + getTemplate() + "/img/tooltip.gif' />";
      }
docs: This method show a tooltip if the key is defined
  
  @param key Key