https://source.android.com/ 
public interface android.telecom.Call$RttCall$RttAudioMode extends java.lang.annotation.Annotation
  minor version: 0
  major version: 59
  flags: flags: (0x2601) ACC_PUBLIC, ACC_INTERFACE, ACC_ABSTRACT, ACC_ANNOTATION
  this_class: android.telecom.Call$RttCall$RttAudioMode
  super_class: java.lang.Object
{
}
SourceFile: "Call.java"
NestHost: android.telecom.Call
InnerClasses:
  public final RttCall = android.telecom.Call$RttCall of android.telecom.Call
  public abstract RttAudioMode = android.telecom.Call$RttCall$RttAudioMode of android.telecom.Call$RttCall
    RuntimeVisibleAnnotations: 
      java.lang.annotation.Retention(value = java.lang.annotation.RetentionPolicy.SOURCE:Ljava/lang/annotation/RetentionPolicy;)