PageTitle.php

<?php

namespace Drupal\Core\Render\Element;

use Drupal\Core\Render\Attribute\RenderElement;

/**
 * Provides a render element for the title of an HTML page.
 *
 * This represents the title of the HTML page's body.
 */
class PageTitle extends RenderElementBase {
    
    /**
     * {@inheritdoc}
     */
    public function getInfo() {
        return [
            '#theme' => 'page_title',
            // The page title: either a string for plain titles or a render array for
            // formatted titles.
'#title' => NULL,
        ];
    }

}