public function Controller_Add($Sender) {
      $Sender->AddSideMenu('settings/tagging');
      $Sender->Title('Add Tag');
      
      // Set the model on the form.
      $TagModel = new TagModel;
      $Sender->Form->SetModel($TagModel);
      
      if ($Sender->Form->AuthenticatedPostBack()) {
         // Make sure the tag is valid
         $TagName = $Sender->Form->GetFormValue('Name');
         if (!TagModel::ValidateTag($TagName))
            $Sender->Form->AddError('@'.T('ValidateTag', 'Tags cannot contain commas.'));
         
         // Make sure that the tag name is not already in use.
         if ($TagModel->GetWhere(array('Name' => $TagName))->NumRows() > 0) {
            $Sender->Form->AddError('The specified tag name is already in use.');
         }
         
         $Saved = $Sender->Form->Save();
         if ($Saved)
            $Sender->InformMessage(T('Your changes have been saved.'));
      }
      
      $Sender->Render('addedit', '', 'plugins/Tagging');
   }