code: public function updateSearchableFields(&$fields) {
  
  		// Instantiate a field containing the existing tags.
  
  		$fields = array_merge(array(
  			'Tagging' => array(
  				'title' => 'Tags',
  				'field' => ListboxField::create(
  					'Tagging',
  					'Tags',
  					FusionTag::get()->map('Title', 'Title')->toArray(),
  					(Controller::has_curr() && ($filtering = Controller::curr()->getRequest()->getVar('q')) && isset($filtering['Tagging'])) ? $filtering['Tagging'] : array(),
  					null,
  					true
  				),
  				'filter' => $this->owner->dbObject('Tagging')->stat('default_search_filter_class')
  			)
  		), $fields);
  
  		// Allow extension.
  
  		$this->owner->extend('updateTaggingExtensionSearchableFields', $fields);
  	}
docs: Update the searchable fields and model admin filtering, allowing CMS searchable content tagging.