Moodle action menus follow almost all the WCAG Menu and Menubar Pattern specifications.

https://www.w3.org/WAI/ARIA/apg/patterns/menubar/

However, we are not yet following the WCAG recommendations for tabindex and aria-activedescendants pertaining to compound components.

Menu items should have their tabindex set to -1, and when focused, should set the menu  "aria-activedescendant" attribute. Here is a quote from the official WCAG page:

One of the following approaches is used to enable scripts to move focus among items in a menu as described in the practice for Keyboard Navigation Inside Components:

• The menu container has tabindex set to -1 or 0 and aria-activedescendant set to the ID of the focused item.
• Each item in the menu has tabindex set to -1, except in a menubar, where the first item has tabindex set to 0.

This issue is about incorporating one of those into the current action menu logic.

More information:

https://www.w3.org/WAI/ARIA/apg/practices/keyboard-interface/#kbd_focus_activedescendant