code: private void purgeExpiredDocuments() {
          // Aligning with database/document change notification to avoid race condition
          // between ending transaction and handling change notification when the documents
          // are purged
          scheduleOnPostNotificationExecutor(
              new Runnable() {
                  @Override
                  public void run() {
                      final int nPurged = getC4Database().purgeExpiredDocs();
                      Log.v(DOMAIN, "Purged %d expired documents", nPurged);
                      scheduleDocumentExpiration(1000);
                  }
              },
              0);
      }
docs: #pragma mark - EXPIRATION: