5.2.5 Required Owned Elements:

Any element that will be owned by the element with this role. For example, an element with the role list will own at least one element with the role group or listitem.

As a non-native English speaker, this first sentence doesn't make sense to me. It doesn't seem to say anything, rather it seems like an unfinished sentence. As though what it should have been is "Any element that will be owned by the element with this role MUST be one of the required owned elements", but the sentence got clipped.

Then in the second sentence it says "will own at least", even though that is followed by a paragraph explaining how there are cases where a list can be empty. Which strongly implies that something like this would be fine:

<div role="list">
  <div role="listitem">List item</div>
  <div> not a list item</div>
</div>

This "at least one" is especially confusing. Should this have been all owned elements SHOULD have a role from the required owned elements list?