Clarify composite inject/extract optional arguments (#1541)

Co-authored-by: Armin Ruech <[email protected]>
Co-authored-by: Carlos Alberto Cortez <[email protected]>

CHANGELOG.md

@@ -7,6 +7,10 @@ release.
 
 ## Unreleased
 
+### Context
+
+- Clarify composite `TextMapPropagator` method required and optional arguments. ([#1541](https://github.com/open-telemetry/opentelemetry-specification/pull/1541))
+
 ### Traces
 
 - Add `ForceFlush` to `Span Exporter` interface ([#1467](https://github.com/open-telemetry/opentelemetry-specification/pull/1467))

specification/context/api-propagators.md

@@ -266,6 +266,9 @@ Required arguments:
 
 - A `Context`.
 - The carrier that holds propagation fields.
+
+If the `TextMapPropagator`'s `Extract` implementation accepts the optional `Getter` argument, the following arguments are REQUIRED, otherwise they are OPTIONAL:
+
 - The instance of `Getter` invoked for each propagation key to get.
 
 ### Composite Inject
@@ -274,6 +277,9 @@ Required arguments:
 
 - A `Context`.
 - The carrier that holds propagation fields.
+
+If the `TextMapPropagator`'s `Inject` implementation accepts the optional `Setter` argument, the following arguments are REQUIRED, otherwise they are OPTIONAL:
+
 - The `Setter` to set a propagation key/value pair. Propagators MAY invoke it multiple times in order to set multiple pairs.
 
 ## Global Propagators