YUI recommends YUI 3.
YUI 2 has been deprecated since 2011. This site acts as an archive for files and documentation.
A common use case for the Panel Control involves using it to display "please wait" text and images to indicate that the application is busy doing something. As this page loads, a modal "please wait"-style Panel Control instance appears and the remainder of the page dims. When the content for the container is loaded (consisting of lorem ipsum text), the panel and its modaliy mask fade away and the page returns to a normal interactive state.