code: public void writeExtractedMsgs(
        SoyMsgBundle msgBundle,
        OutputFileOptions options,
        ByteSink output,
        ErrorReporter errorReporter)
        throws IOException {
  
      CharSequence cs = msgPlugin.generateExtractedMsgsFile(msgBundle, options, errorReporter);
      output.asCharSink(UTF_8).write(cs);
    }
docs: Generates extracted messages (source messages to be translated) from a given message bundle,
  and writes it out.
  
  <p>Important: Do not use outside of Soy code (treat as superpackage-private).
  
  @param msgBundle The message bundle to write.
  @param options The options for generating the output extracted messages (depending on the
  message plugin being used, none or some of the options may be applicable).
  @param output The output to write to.
  @param errorReporter For reporting errors.
  @throws SoyMsgException If there's an error while processing the messages.
  @throws IOException If there's an error writing the messages.