Specify destination name for RabbitMQ

docs/messaging/rabbitmq.md

@@ -12,8 +12,15 @@ The Semantic Conventions for [RabbitMQ](https://www.rabbitmq.com/) extend and ov
 
 ## RabbitMQ attributes
 
+### Destination name
+
 In RabbitMQ, the destination is defined by an *exchange* and a *routing key*.
-`messaging.destination.name` MUST be set to the name of the exchange. This will be an empty string if the default exchange is used.
+`messaging.destination.name` MUST be set according to the following rules:
+
+- Both *exchange* and *routing key* present and non-empty: `{exchange}:{routing key}`
+- Only *exchange* present and non-empty: `{exchange}`
+- Only *routing key* present and non-empty: `{routing key}`
+- Otherwise: `amp.default`
 
 <!-- semconv messaging.rabbitmq -->
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