code: public final IonTextWriterBuilder withLongStringThreshold(int threshold)
      {
          IonTextWriterBuilder b = mutable();
          b.setLongStringThreshold(threshold);
          return b;
      }
docs: Declares the length beyond which string and clob content will be rendered
  as triple-quoted "long strings".
  At present, such content will only line-break on extant newlines.
  
  @param threshold the new threshold; zero means none.
  
  @see #getLongStringThreshold()
  @see #setLongStringThreshold(int)
  
  @return this instance, if mutable;
  otherwise a mutable copy of this instance.