Update airbyte-protocol.md (#13892)

* Update airbyte-protocol.md

* Fix typo

* Fix prose

* Add protocol reviewers for protocol documentation

* Remove duplicate

.github/CODEOWNERS

@@ -4,4 +4,6 @@
 ## Exclude the package(-lock).json from code ownership to prevent version bump PRs from triggering codeowners review
 /airbyte-webapp/package.json
 /airbyte-webapp/package-lock.json
+# Protocol related items
 /airbyte-protocol/ @airbytehq/protocol-reviewers
+/docs/understanding-airbyte/airbyte-protocol.md @airbytehq/protocol-reviewers

docs/understanding-airbyte/airbyte-protocol.md

@@ -449,7 +449,11 @@ For forwards compatibility all messages should allow for unknown properties (in
 Messages are structs emitted by actors.
 
 ### StreamDescriptor
-A stream descriptor contains all information required to identify a Stream. `namespace` can be null if the stream does not have an associated namespace. If it does, it must be populated. `name` is required.
+A stream descriptor contains all information required to identify a Stream:
+
+* The `name` of the stream (required).  It may not be `null`.
+* The `namespace` of the stream (optional).  It may be `null` if the stream does not have an associated namespace, otherwise must be populated.
+* Any UTF-8 string value is valid for both `name` and `namespace`, including the empty string (`""`) value.
 
 This is the new pattern for referring to a stream. As structs are updated, they are moved ot use this pattern. Structs that have not been updated still refer to streams by having top-level fields called `stream_name` and `namespace`.