Section 508 Reference Guide - Navigation of EAST Panes with a Keyboard
Using ARROW keys to navigate the Tree View in Pane 1 (upper left pane) sometimes causes focus to switch to Pane 2 (upper right pane) unexpectedly. This can be disorienting for the user.
Using the keyboard, a user should be able to navigate between each of the three panes. A keyboard user can navigate into Pane 3 (lower pane), but cannot navigate back to Pane 1 or Pane 2.