Pages in the Docked state appear against a control edge. In the following
image you can see that two pages are docked against the left edge of the
client area.

By pressing the pin button on the docked caption bar the pages are
switched to the AutoHidden state. The following image shows the two
pages as just tabs placed on the edge of the client area.

If you hover the mouse over an AutoHidden tab then a window slides
into view with the contents of that page. Once the mouse moves away
from the tab and page area the window will slide back away from view.