silverstripe-docsviewer/code/forms/DocumentationSearchForm.php

<?php

class DocumentationSearchForm extends Form {

	public function __construct($controller) {


		$fields = new FieldList(
			TextField::create('q', _t('DocumentationViewer.SEARCH', 'Search'), '')
				->setAttribute('placeholder', _t('DocumentationViewer.SEARCH', 'Search'))
		);

		$page = $controller->getPage();

		if($page){
			$versions = HiddenField::create(
				'Versions',
				_t('DocumentationViewer.VERSIONS', 'Versions'),
				$page->getEntity()->getVersion()
			);

			$fields->push($versions);
		}

		$actions = new FieldList(
			new FormAction('results', _t('DocumentationViewer.SEARCH', 'Search'))
		);

		parent::__construct($controller, 'DocumentationSearchForm', $fields, $actions);

		$this->disableSecurityToken();
		$this->setFormMethod('GET');
		$this->setFormAction($controller->Link('results'));

		$this->addExtraClass('search');
	}
}