code: public void sendBroadcast(CmsObject cms, String message, String sessionId, boolean repeat) {
  
          if (CmsStringUtil.isEmptyOrWhitespaceOnly(message)) {
              // don't broadcast empty messages
              return;
          }
          // send the broadcast only to the selected session
          CmsSessionInfo sessionInfo = m_sessionStorageProvider.get(new CmsUUID(sessionId));
          if (sessionInfo != null) {
              // double check for concurrent modification
              sessionInfo.getBroadcastQueue().add(
                  new CmsBroadcast(cms.getRequestContext().getCurrentUser(), message, repeat));
          }
  
      }
docs: Sends a broadcast to the specified user session.<p>
  
  @param cms the OpenCms user context of the user sending the broadcast
  
  @param message the message to broadcast
  @param sessionId the OpenCms session uuid target (receiver) of the broadcast
  @param repeat repeat this message