Initialization must not be part of a batch

Author: jspahrsummers

docs/specification/draft/basic/lifecycle.md

@@ -73,8 +73,11 @@ The client **MUST** initiate this phase by sending an `initialize` request conta
 }
 ```
 
-For backwards compatibility with older protocol versions, the initialize request **SHOULD
-NOT** be part of a JSON-RPC [batch](https://www.jsonrpc.org/specification#batch).
+The initialize request **MUST NOT** be part of a JSON-RPC
+[batch](https://www.jsonrpc.org/specification#batch), as other requests and notifications
+are not possible until initialization has completed. This also permits backwards
+compatibility with prior protocol versions that do not explicitly support JSON-RPC
+batches.
 
 The server **MUST** respond with its own capabilities and information: