Change 605673 had a related patch set uploaded (by Bkudiess-msft; owner: Bkudiess-msft):
[oojs/ui@master] Tool: Fixes narrator not announcing count of items on dropdown menu

https://gerrit.wikimedia.org/r/605673

Repeating from patch set, @Bkudiess-msft please expand a bit more on the role parent > child relationship and what is missing, what would be gained and how to tailor this to the general library and Tool applications. With that patch we would change <a> to role=option and this is not allowed for <a> elements. Was too quick in my comment on patch with contradiction of <a> and role="option". It's actually allowed, which preceeded ARIA 1.1 and were now allowed. Though we might have tools not carrying <a> as element.
See for example VisualEditor's use of tools in the toolbar. https://en.wikipedia.org/wiki/Front_end?veaction=edit

@Volker_E For example, is you go to "Switch Editor" button with a screen reader turned on, and expand it, once you focus moves to any of the elements in the dropdown menu, it should announce "Visual Editing 1 of 2" or "Source editing 2 of 2", so visually impaired users might know how many items exist on the list and how far along they are.
If you change the role to be "option" it does the work for you counting the elements contained in the dropdown menu.

@Bkudiess-msft Is this role=option behaviour applying to Narrator only? Or across products?

@Volker_E I usually use Narrator and NVDA for testing, but this feature I could only see in Narrator for now.

And with role=option it continues to be useful exposed in NVDA? Need to test in VO.

Change 605673 abandoned by VolkerE:
[oojs/ui@master] Tool: Fixes narrator not announcing count of items on dropdown menu

Reason:
Abandoned due to inactivity on crucial feedback (ARIA role value change). Please feel free to re-open with new insights.

https://gerrit.wikimedia.org/r/605673