当你在回答一个问题而有人提交了另一个答案时，stackoverflow上显示的弹出警告是如何显示的?

Ok, so you know when you're answering a question and are in the middle of typing it, and someone else posts an answer to your question and you get a little popup that says there is a new answer to the question? My question is how do you do that? I think I have the basic concept down... A question is answered, added to the database. The page your on keeps checking the database for new answers, and if there is something new displays a popup. (I'm not sure if that's how it's done, but just and idea) Anyway, I'm trying to create an application with similar functionality to that popup using php, and jQuery / Ajax / something else? I have a page that will be on the screen and will display information from the database. What I need: to figure out how to get that popup to display only when there is new content added to the database. Thanks for the help!Ok, so you know when you're answering a questio