code: public function updateSearchForm($form) {
  
  		// Update the page filtering, allowing multiple tags.
  
  		Requirements::javascript(FUSION_PATH . '/javascript/fusion.js');
  
  		// Instantiate a field containing the existing tags.
  
  		$form->Fields()->insertBefore(ListboxField::create(
  			'q[Tagging]',
  			'Tags',
  			FusionTag::get()->map('Title', 'Title')->toArray(),
  			(($filtering = $this->owner->getRequest()->getVar('q')) && isset($filtering['Tagging'])) ? $filtering['Tagging'] : array(),
  			null,
  			true
  		), 'q[Term]');
  
  		// Allow extension.
  
  		$this->owner->extend('updateCMSMainTaggingExtensionSearchForm', $form);
  	}
docs: Update the page filtering, allowing CMS searchable content tagging.