Add a directive that the Baggage API must function, even without an S…

…DK. (#1103)

* Add a directive that the Baggage API must function, even without an SDk.

* add the changelog entry

* add a missing CR

CHANGELOG.md

@@ -9,6 +9,8 @@ release.
 
 New:
 
+- Enforce that the Baggage API must be fully functional, even without an installed SDK.
+  ([#1103](https://github.com/open-telemetry/opentelemetry-specification/pull/1103))
 - Rename "Canonical status code" to "Status code"
   ([#1081](https://github.com/open-telemetry/opentelemetry-specification/pull/1081))
 - Add Metadata for Baggage entries, and clarify W3C Baggage Propagator implementation

specification/baggage/api.md

@@ -33,6 +33,10 @@ into the context. The [Get all](#get-all) function could be implemented by retur
 object as a whole from the function call. If an idiom like this is implemented, the Baggage object/struct
 MUST be immutable, so that the containing Context also remains immutable.
 
+The Baggage API MUST be fully functional in the absence of an installed SDK. This is required in
+order to enable transparent cross-process Baggage propagation. If a Baggage propagator is installed
+into the API, it will work with or without an installed SDK.
+
 ### Baggage
 
 `Baggage` is used to annotate telemetry, adding context and information to metrics, traces, and logs.