https://developers.google.com/protocol-buffers/protobuf-java/: Core Protocol Buffers library. Protocol Buffers are a way of encoding structured data in an efficient yet extensible format. 
public interface com.google.protobuf.ProtocolMessageEnum extends com.google.protobuf.Internal$EnumLite
  minor version: 0
  major version: 59
  flags: flags: (0x0601) ACC_PUBLIC, ACC_INTERFACE, ACC_ABSTRACT
  this_class: com.google.protobuf.ProtocolMessageEnum
  super_class: java.lang.Object
{
  public abstract int getNumber();
    descriptor: ()I
    flags: (0x0401) ACC_PUBLIC, ACC_ABSTRACT

  public abstract com.google.protobuf.Descriptors$EnumValueDescriptor getValueDescriptor();
    descriptor: ()Lcom/google/protobuf/Descriptors$EnumValueDescriptor;
    flags: (0x0401) ACC_PUBLIC, ACC_ABSTRACT

  public abstract com.google.protobuf.Descriptors$EnumDescriptor getDescriptorForType();
    descriptor: ()Lcom/google/protobuf/Descriptors$EnumDescriptor;
    flags: (0x0401) ACC_PUBLIC, ACC_ABSTRACT
}
SourceFile: "ProtocolMessageEnum.java"
InnerClasses:
  public final EnumDescriptor = com.google.protobuf.Descriptors$EnumDescriptor of com.google.protobuf.Descriptors
  public final EnumValueDescriptor = com.google.protobuf.Descriptors$EnumValueDescriptor of com.google.protobuf.Descriptors
  public abstract EnumLite = com.google.protobuf.Internal$EnumLite of com.google.protobuf.Internal