code: FormattingContext concat(FormattingContext other) {
      if (isEmpty()) {
        return other;
      } else if (other.isEmpty()) {
        return this;
      } else {
        curIndent = ""; // don't serialize trailing whitespace in front of the next FormattingContext.
        return append(other.toString());
      }
    }
docs: Returns a FormattingContext representing the concatenation of this FormattingContext with
  {@code other}. For use only by {@link CodeChunk#getCode(int, OutputContext)}.