[focusgroup] How does focusgroup interplay with autofocus?

In https://github.com/openui/open-ui/issues/989 we discussed a scenario for orthogonal focus groups; say you have something like:

<div focusgroup=horizontal>
  <button></button>
  <button invoketarget=more-menu>More</button>
  <div popover id=more-menu focusgroup=vertical>
    <button autofocus></button>    
  </div>
</div>

Supposedly, opening the popover menu would land focus on the button, and then the vertical group would focus? What happens in light of the resolutions in https://github.com/openui/open-ui/issues/989 where the element with focusgroup is part of the group?

Perhaps also interesting, what if we change from invoketarget to interesttarget?

<div focusgroup=horizontal>
  <button></button>
  <button interesttarget=more-menu>More</button>
  <div popover id=more-menu focusgroup=vertical>
    <button autofocus></button>    
  </div>
</div>

Start by reading the resolutions in openui/open-ui#989, then compare the invoketarget and interesttarget examples in this issue. Determine how focusgroup and autofocus interact when the popover opens, and document the resulting behavior or required resolution for both cases.