code: public final _Private_IonTextWriterBuilder
                   withCallbackBuilder(_Private_CallbackBuilder builder)
      {
          _Private_IonTextWriterBuilder b = mutable();
          b.setCallbackBuilder(builder);
          return b;
      }
docs: Declares the {@link _Private_CallbackBuilder} to use when building.
  @param builder
  The builder that will be used to build a new MarkupCallback.
  @return this instance, if mutable; otherwise a mutable copy of this
  instance.
  @see #getCallbackBuilder()
  @see #setCallbackBuilder(_Private_CallbackBuilder)