Refine the handling of OTEL_RESOURCE_ATTRIBUTES. (#4856)

Fixes #4847 

* Fail fast, e.g. discard the ENTIRE env var value in the case of an
error.
* Values outside the baggage-octet (an ANSI subset) SHOULD be percent
encoded, rather than MUST.

---------

Co-authored-by: Reiley Yang <[email protected]>

Author: carlosalberto

CHANGELOG.md

@@ -29,6 +29,9 @@ release.
 
 ### Resource
 
+- Refine the handling of OTEL_RESOURCE_ATTRIBUTES.
+  ([#4856](https://github.com/open-telemetry/opentelemetry-specification/pull/4856))
+
 ### Entities
 
 ### Common

specification/resource/sdk.md

@@ -182,11 +182,15 @@ information provided by the user, i.e. the user provided resource information
 has higher priority.
 
 The `OTEL_RESOURCE_ATTRIBUTES` environment variable will contain of a list of
-key value pairs, and these are expected to be represented in a format matching
-to the [W3C Baggage](https://www.w3.org/TR/baggage/#header-content), except that additional
-semi-colon delimited metadata is not supported, i.e.: `key1=value1,key2=value2`.
-All attribute values MUST be considered strings and characters outside the
-`baggage-octet` range MUST be percent-encoded.
+key value pairs, represented as `key1=value1,key2=value2`.
+All attribute values MUST be considered strings. The `,` and `=` characters
+in keys and values MUST be percent encoded. Other characters MAY be
+[percent-encoded](https://datatracker.ietf.org/doc/html/rfc3986#section-2.1),
+e.g. values outside the ANSI characters set.
+
+In case of any error, e.g. failure during the decoding process, the entire environment
+variable value SHOULD be discarded and an error SHOULD be reported following the
+[Error Handling principles](../error-handling.md#basic-error-handling-principles).
 
 ## Resource operations