The way drawCustomFocusRing appears to work is to give accessibility devices the location of the fallback element, and to signal to the dev to draw something. 

I'm thinking that we could have a focus ring object that contains attributes for color, transparency, line type, and possibly some other visual attributes such as pattern or image. 

It would be tied to the fallback element, as well as a specific path (might work best with the Path object). There could be more than one focus ring object defined to allow rings to be drawn in different colors to compensate for different background colors. 

The benefit would be a standard but changeable focus ring display.