@java.lang.Override
  public void writeTo(com.google.protobuf.CodedOutputStream output) throws java.io.IOException {
    if (!com.google.protobuf.GeneratedMessageV3.isStringEmpty(role_)) {
      com.google.protobuf.GeneratedMessageV3.writeString(output, 1, role_);
    }
    for (int i = 0; i < parts_.size(); i++) {
      output.writeMessage(2, parts_.get(i));
    }
    getUnknownFields().writeTo(output);
  }
<pre>
Required. Ordered `Parts` that constitute a single message. Parts may have
different IANA MIME types.
</pre>

<code>
repeated .google.cloud.vertexai.v1.Part parts = 2 [(.google.api.field_behavior) = REQUIRED];
</code>
java-vertexai/proto-google-cloud-vertexai-v1/src/main/java/com/google/cloud/vertexai/api/Content.java