let's say i have the following HTML page.

```
<A panel to display list of items>
  Item A
  Item B
  Item C
  ...

<A panel to display details about item>
  Details on item X:

```

I want to write the page so that whenever the user clicks on one of the items, the detail about the selected item will show up on the bottom panel.

However, few problems that I want to solve are:

* How should I prevent duplicate requests. (like, user presses links to item A and B before the detail of item A returns from the server).
* If I want to display "detail is now loading...", where should I put the code?