keyboard access to split panes, especially hierarchical splits

I'm finding lots of problems with keyboard-only access to split panes:

- If I have hierarchical split panes, I cannot figure out how to get F8 to get focus to the parent splitter bar. and I cannot figure out how to get F6 to put focus into the "aunt" (sibling of parent) pane.

- If I put focus on the splitter bar with F8, I can't figure out how to get focus back to where it had been before.

- With the mouse, the user can use those little arrows in the splitter bar to jump the splitter-bar all the way to one side, and then jump back to where the bar had been. With the keyboard, Home and End jump the bar to one side, but there doesn't appear to be any easy way to move the bar back to where it had been.