code: private EnumConstantElement readEnumConstant(
        String documentation, Location location, String label) {
      reader.require('=');
  
      int tag = reader.readInt();
  
      List<OptionElement> options = new OptionReader(reader).readOptions();
      reader.require(';');
      documentation = reader.tryAppendTrailingDocumentation(documentation);
  
      return new EnumConstantElement(
          location,
          label,
          tag,
          documentation,
          options);
    }
docs: Reads an enum constant like "ROCK = 0;". The label is the constant name.