clarify relationship with deprecated

Author: davidjgoss

proposals/2020-10-28-Experimental.md

@@ -113,12 +113,13 @@ This kind of requirement is handled for TypeScript libraries by [api-extractor](
 ### Unanswered Questions
 
 - If an operation is not marked as experimental, but it is using a schema which is (i.e. as its request object), then it is implicitly also unstable. Would this usage be considered invalid?
-- Should `experimental` and `deprecated` be mutually exclusive?
 
 ## Backwards compatibility
 
 The `experimental` field would default to false, meaning existing behaviour is preserved, and the new field is only used on an opt-in basis.
 
+`experimental` can coexist with `deprecated` - an operation, parameter or schema can be both experimental and deprecated, having never gotten to a stable point before being deprecated.
+
 ## Alternatives considered
 
 - _Specification extensions_ - publishers could add an extension in their own domain, but the benefit of the metadata being available to downstream tools (including those used by consumers, not just publishers) would be lost.