code: public boolean isValid(TagData data) {
          TagExtraInfo tei = getTagExtraInfo();
          if (tei == null) {
  	    return true;
          }
          return tei.isValid(data);
      }
docs: Translation-time validation of the attributes.
  This is a convenience method on the associated TagExtraInfo class.
  
  @param data The translation-time TagData instance.
  @return Whether the data is valid.