@NellWaliczek brought this up in the meeting

Basically, we should explicitly specify an internal "natural origin" or "pose" ("transform"?) related to each kind of XR Space. This transform is relative to some implementation-defined internal global origin consistent across spaces (what this origin is doesn't really matter since it's never exposed -- users can only query the relationship between two spaces).

This should clarify #565 and #581 and a bunch of other issues that are floating around.

I don't mind working on this if folks think this is valuable to try (perhaps worth waiting for #587 and #589 first?)