docs: public SanitizedContent knownDirAttrSanitized(Dir dir) {
      Preconditions.checkNotNull(dir);
      if (dir != contextDir) {
        switch (dir) {
          case LTR:
            return LTR_DIR;
          case RTL:
            return RTL_DIR;
          case NEUTRAL:
            // fall out.
        }
      }
      return NEUTRAL_DIR;
    }