Clarify usage of log body for structured logs (open-telemetry#3023)

See decision by Log SIG noted in [open-telemetry#3014](open-telemetry#3014 (comment))

CHANGELOG.md

@@ -78,6 +78,8 @@ release.
   ([#2969](https://github.com/open-telemetry/opentelemetry-specification/pull/2969))
 - Make sure it is very clear we are not building a Logging API.
   ([#2966](https://github.com/open-telemetry/opentelemetry-specification/pull/2966))
+- Clarify usage of log body for structured logs
+  ([#3023](https://github.com/open-telemetry/opentelemetry-specification/pull/3023))
 
 ### Resource
 

specification/logs/data-model.md

@@ -419,9 +419,10 @@ Description: A value containing the body of the log record (see the description
 of `any` type above). Can be for example a human-readable string message
 (including multi-line) describing the event in a free form or it can be a
 structured data composed of arrays and maps of other values. First-party
-Applications SHOULD use a string message. However, a structured body may be
-necessary to preserve the semantics of some existing log formats. Can vary for
-each occurrence of the event coming from the same source. This field is optional.
+Applications SHOULD use a string message. However, a structured body SHOULD be
+used to preserve the semantics of structured logs emitted by Third-party
+Applications. Can vary for each occurrence of the event coming from the same
+source. This field is optional.
 
 ### Field: `Resource`