Scrollable regions

Hello

I’m aware that embedded scrollable regions can cause difficulty for voice activation users and usually avoid them wherever possible.

I know that where they are used, the scrollable region needs to be focusable for it to be able to be operated via the use of the keyboard (or else the region needs to contain a focusable element). Otherwise, I would consider this a 2.1.1 keyboard fail. Is this correct?

However, I have just encountered a scrollbar on an empty region. This controls a different region via a JS scroll event. If this is made focusable, I think it will be ambiguous to screen reader users as the association between the scrollbar and the region it controls is not clear. Therefore, I am looking into the aria scrollbar role and have some questions:

1. Is this intended for all embedded scrolls created using css overflow property?
2. How do I calculate the aria-valuenow? Is it 0 when the scrollbar is all the way to the left (for a horizontal scroll) and 100 when it is all the way to the right?

Thanks

Sarah