Visual and physical disconnect when using keyboard nav with movers in vertical configuration.

[talldan]

Describe the bug
Recently, arrow key navigation was introduced to the Block Toolbar, a really positive feature, since it makes the toolbar a single tab stop.

I noticed that the left and right arrow keys are used to navigate a toolbar, but when the block movers are in their vertical configuration it doesn't feel right to use left/right:

Here, I want to press up and down to switch between the buttons. Pressing up/down unfortunately results in the toolbar losing focus, I think it triggers navigation between blocks.

Technically, left and right is probably correct for the DOM order, but I found it caused a disconnect for those navigating based on the visual positioning.

I also discovered the same in #22314.

To reproduce
Steps to reproduce the behavior:

1. Add a navigation block
2. Add navigation links with multiple levels of nesting
3. Select a deeply nested navigation link and try navigating the toolbar using the keyboard

Expected behavior
Not sure!

[talldan]

cc @diegohaz I know this is something you worked on. Was wondering what your thoughts are about this?

[diegohaz]

I also expect vertical keys to work when navigating through the toolbar movers with keyboard. At first, I don't see any problems with doing that (as long as the horizontal keys still work).

I've tried to find a reference on native or web widgets with this kind of behavior, but all of them seem to just ignore the visual representation. For example, on MacOS/Chrome menus, you only navigate using vertical keys, even though you have a lot of items represented horizontally in the UI:

The WAI-ARIA Authoring Practices have this example on layout grids where you can navigate through search result articles using arrow keys. To select the description paragraph, you have to use the right arrow keys, even though it's visually in a new row:

In the markup, each article represents a grid row with 3 cells, so it makes sense for screen reader users.

[diegohaz]

As you mentioned, the toolbar loses focus and gets hidden when you use up/down arrow keys, which makes this expectation break even more harmful.