Clean up implementation guidelines for environment variable propagation carriers

CHANGELOG.md

@@ -15,6 +15,9 @@ release.
 - Specify that environment variable propagation carriers only read and return
   normalized environment variable names.
   ([#5144](https://github.com/open-telemetry/opentelemetry-specification/pull/5144))
+- Clean up implementation guidelines for environment variable propagation
+  carriers.
+  ([#5166](https://github.com/open-telemetry/opentelemetry-specification/pull/5166))
 
 ### Traces
 

specification/context/env-carriers.md

@@ -14,7 +14,7 @@
     + [Environment Variable Immutability](#environment-variable-immutability)
     + [Process Spawning](#process-spawning)
     + [Security](#security)
-- [Supplementary Guidelines](#supplementary-guidelines)
+- [Implementation Guidelines](#implementation-guidelines)
 
 <!-- tocstop -->
 
@@ -130,11 +130,11 @@ process and with the correct permissions, can be accessed from other processes.
   environment variables may be visible to other processes or users with
   appropriate permissions.
 
-## Supplementary Guidelines
+## Implementation Guidelines
 
 > [!IMPORTANT]
-> This section is non-normative and provides implementation
-> guidance only. It does not add requirements to the specification.
+> This section is non-normative and provides implementation guidance only. It
+> does not add requirements to the specification.
 
 Language implementations of OpenTelemetry have flexibility in how they expose
 environment variable context propagation. The existing `TextMapPropagator` can
@@ -145,28 +145,28 @@ that implement these operations themselves. Whichever component performs `Get`,
 `Set`, or `Keys` for environment variables is responsible for the normalization
 behavior described above. Language-specific helper components are only expected
 to operate on the carrier shapes supported by that language implementation.
-Implementations commonly provide one or more of the following:
 
-- `Getter` - creates an in-memory copy of the current environment variables and
-  reads context from that copy.
-- `Setter` - writes context to a dictionary/map and provides the dictionary/map
-  to the application owner for them to use when spawning processes.
-- An environment-specific carrier type - implements environment variable `Get`,
-  `Set`, or `Keys` operations directly when the language combines carrier and
-  accessor APIs.
+Implementations may consider a caching behavior that fits their API shape. For
+example, an implementation can:
 
-Examples:
+- Load environment variables whose names are already normalized into a cache
+  during initialization or on first use.
+- Cache the results of individual `Get` lookups by normalized key.
+
+Example implementations:
 
 - [OpenTelemetry .NET implementation][di]
 - [OpenTelemetry C++ implementation][ci]
 - [OpenTelemetry Go implementation][gi]
 - [OpenTelemetry Java implementation][ji]
+- [OpenTelemetry JavaScript implementation][jsi]
 - [OpenTelemetry Python implementation][pi]
 - [OpenTelemetry Swift implementation][si]
 
 [di]: https://github.com/open-telemetry/opentelemetry-dotnet/blob/main/src/OpenTelemetry.Api/Context/Propagation/EnvironmentVariableCarrier.cs
 [ci]: https://github.com/open-telemetry/opentelemetry-cpp/blob/main/api/include/opentelemetry/context/propagation/environment_carrier.h
 [gi]: https://github.com/open-telemetry/opentelemetry-go-contrib/tree/main/propagators/envcar
 [ji]: https://github.com/open-telemetry/opentelemetry-java/tree/main/api/incubator/src/main/java/io/opentelemetry/api/incubator/propagation
+[jsi]: https://github.com/open-telemetry/opentelemetry-js/tree/main/experimental/packages/opentelemetry-propagator-env-carrier
 [pi]: https://github.com/open-telemetry/opentelemetry-python/blob/main/opentelemetry-api/src/opentelemetry/propagators/_envcarrier.py
 [si]: https://github.com/open-telemetry/opentelemetry-swift-core/blob/main/Sources/OpenTelemetrySdk/Trace/Propagation/EnvironmentContextPropagator.swift