public function Bookmark($ConversationID = '', $TransientKey = '') {
      $Session = Gdn::Session();
      $Success = FALSE;
      $Star = FALSE;
      
      // Validate & do bookmarking
      if (
         is_numeric($ConversationID)
         && $ConversationID > 0
         && $Session->UserID > 0
         && $Session->ValidateTransientKey($TransientKey)
      ) {
         $Bookmark = $this->ConversationModel->Bookmark($ConversationID, $Session->UserID);
      }
      
      // Report success or error
      if ($Bookmark === FALSE)
         $this->Form->AddError('ErrorBool');
      else
         $this->SetJson('Bookmark', $Bookmark);
      
      // Redirect back where the user came from if necessary
      if ($this->_DeliveryType == DELIVERY_TYPE_ALL)
         Redirect($_SERVER['HTTP_REFERER']);
      else
         $this->Render();
   }