This change adds an admonition to document the fact that every role can only ever be assigned to a single group at the same time. Since this is surprising based on a traditional understanding of role-based models, I've decided to make this a `:::warning`.
I'm undecided on the best place for this information, but for now, decided on putting it into the context of the action that can fail: assigning a role to a group.
While this does not close the issue, it documents this behavior to at least address the "needs documentation" aspect of #10983 .
Signed-off-by: Zuri Klaschka <pklaschka@users.noreply.github.com>
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