如何在html中的图标上显示简单的工具提示？

I am using ActiveScaffold in a Ruby on Rails app, and to save space in the table I have replaced the default "actions" text in the table (ie. "edit", "delete", "show") with icons using CSS. I have also added a couple of custom actions with action_link.add ("move" and "copy").I am using ActiveScaffold in a Ruby on Rails ap