code: public final LoggingAdvisingAppendable setSanitizedContentDirectionality(@Nullable Dir contentDir)
        throws IOException {
      if (!contentDirSet) {
        contentDirSet = true;
        this.contentDir = contentDir;
        notifyContentDirectionality(contentDir);
      }
      return this;
    }
docs: Marks the directionality of this appendable. All the {@link #append} commands should be
  considered to be content of the given directionality that has already been sanitized.
  
  <p>Calls after the first call to this are ignored.