code: private boolean isExpired( DBCollection content,
                                 long deadline ) {
          Long unusedSince = (Long)getAttribute(content, FIELD_UNUSED_SINCE);
          return unusedSince != null && unusedSince < deadline;
      }
docs: Checks status of unused content.
  
  @param content content to check status
  @param deadline moment of time in past
  @return true if content is marked as unused before the deadline