The 2.14 release announcement sounds like it already has this feature:

http://myronmars.to/n/dev-blog/2013/07/rspec-2-14-is-released#core_shared_example_groups_are_scoped_to_the_context_they_are_defined_in

Maybe this should say:

```
* Disallow use of a shared example group from a sibling context,
  fully isolating them between contexts.
  2.14 and 2.99 allowed this but printed a deprecation warning. (Jon Rowe)
```