The Accordion (panelBar from 3.3.x) is a set of panels when one panel is expanded, but other ones are collapsed.

Main addition to previous 3.3.x functionality - accordion in 4.x was finally added with different switching switchType's. So as all the switchable panels it could be used with next modes - "client", "ajax" and "server".

The following demo shows the simple example of usage for the Accordion in client mode: