Added comment

Author: ValentinZakharov

internal-api/src/main/java/datadog/trace/bootstrap/instrumentation/api/SpanWrapper.java

@@ -1,5 +1,10 @@
 package datadog.trace.bootstrap.instrumentation.api;
 
+/**
+ * Interface implemented by span wrappers such as OpenTelemetry and OpenTracing spans.
+ * Provides a callback that is invoked when the underlying span is finished.
+ * This guarantees that wrapper specific logic runs when spans are auto-finished.
+ */
 public interface SpanWrapper {
   default void onSpanFinished() {}
 }