@java.lang.Override
  public void writeTo(com.google.protobuf.CodedOutputStream output) throws java.io.IOException {
    for (int i = 0; i < phraseSets_.size(); i++) {
      output.writeMessage(1, phraseSets_.get(i));
    }
    for (int i = 0; i < phraseSetReferences_.size(); i++) {
      com.google.protobuf.GeneratedMessageV3.writeString(output, 2, phraseSetReferences_.getRaw(i));
    }
    for (int i = 0; i < customClasses_.size(); i++) {
      output.writeMessage(3, customClasses_.get(i));
    }
    if (((bitField0_ & 0x00000001) != 0)) {
      output.writeMessage(4, getAbnfGrammar());
    }
    getUnknownFields().writeTo(output);
  }
<pre>
Augmented Backus-Naur form (ABNF) is a standardized grammar notation
comprised by a set of derivation rules.
See specifications: https://www.w3.org/TR/speech-grammar
</pre>

<code>.google.cloud.speech.v1p1beta1.SpeechAdaptation.ABNFGrammar abnf_grammar = 4;</code>
java-speech/proto-google-cloud-speech-v1p1beta1/src/main/java/com/google/cloud/speech/v1p1beta1/SpeechAdaptation.java