Rename built-in ExemplarFilters

specification/metrics/sdk.md

@@ -658,8 +658,28 @@ This interface SHOULD have access to:
   [Span](../trace/api.md#span).
 - A `timestamp` that best represents when the measurement was taken.
 
-See [Defaults and Configuration](#defaults-and-configuration) for built-in
-filters.
+Sampled here simply makes the measurement eligible for being included as an
+exemplar. `ExemplarReservoir` makes the final decision if a measurement becomes
+an exemplar.
+
+### Built-in ExemplarFilters
+
+OpenTelemetry supports a number of built-in exemplar filters to choose from.
+The default is `SampleWithTrace`.
+
+#### AlwaysOn
+
+An ExemplarFilter which makes all measurements eligible for being an Exemplar.
+
+#### AlwaysOff
+
+An ExemplarFilter which makes no measurements eligible for being an Exemplar.
+Using this ExemplarFilter is as good as disabling Exemplar feature.
+
+#### SampleWithTrace
+
+An ExemplarFilter which makes those measurements eligible for being an
+Exemplar, which are recorded in the context of a sampled parent span.
 
 ### ExemplarReservoir
 

specification/sdk-environment-variables.md

@@ -266,9 +266,9 @@ Known values for `OTEL_LOGS_EXPORTER` are:
 
 Known values for `OTEL_METRICS_EXEMPLAR_FILTER` are:
 
-- `"none"`: No measurements are eligible for exemplar sampling.
-- `"all"`: All measurements are eligible for exemplar sampling.
-- `"with_sampled_trace"`: Only allow measurements with a sampled parent span in context.
+- `"always_on"`: [AlwaysOn](./metrics/sdk.md#alwayssample)
+- `"always_off"`: [AlwaysOff](./metrics/sdk.md#neversample)
+- `"sample_with_trace"`: [SampleWithTrace](./metrics/sdk.md#samplewithtrace)
 
 ### Periodic exporting MetricReader