Review tab order for accessibility

[kmcnaught]

Let's review this together on a call, but I'll highlight some issues

[kmcnaught]

Overall, when all the sidebars are open, the tab order is fairly sensible, but I think there are some improvements to be made. Some areas for discussion...

Navigation from a closed docs sidebar

If you're loading to a small size, the left hand docs sidebar is closed, and the Ref/Ideas/API/Project are skipped from the tab order. This means you can't tab into these areas without expanding the sidebar first - and the screen reader description doesn't signpost what the contents are.

If instead you collapse the sidebar manually, then you get a much nicer tab order, which I think would be reasonable to copy.

Navigation to editor from an open docs sidebar

If the left hand sidebar is open (reference pane open by default), it takes >40 tabs to get to the editor, as you are taken via all the topic buttons. If you are using a screen reader and know all the shortcuts, you can shortcircuit by navigating by region, but it would be preferable to have a more streamlined / nested navigation order, as well as skip-links (see #978)

Navigation from revisited webpage

See discussion in 973 - Reading around this, NVDA by design remembers where the user's last position when returning to a previously visited web page. This isn't working quite as expected with the Python Editor.
Originally posted by @microbit-robert in #973 (comment)

To review further, once we've got to the bottom of 973

Related issues

#973, #978

[microbit-robert]

#982 has fixed the "Navigation from a closed docs sidebar" part of this issue. When using the beta deployment (inside an iFrame), NVDA is causing the focus to switch to different areas of the Editor - this does not occur when running the project locally (not in an iFrame).