C14N example

$this->host->body->value = $markup;
        $this->host->save();

        $this->drupalGet($this->host->toUrl('edit-form'));
        $this->waitForEditor();

        // Ensure that the image is rendered in preview.         $this->assertNotEmpty($this->assertSession()->waitForElementVisible('css', ".ck-content .ck-widget img"));
        $editor_dom = $this->getEditorDataAsDom();
        $expected_dom = Html::load($expected);
        $xpath = new \DOMXPath($this->getEditorDataAsDom());
        $this->assertEquals($expected_dom->getElementsByTagName('body')->item(0)->C14N(), $editor_dom->getElementsByTagName('body')->item(0)->C14N());

        // Ensure the test attribute is persisted on downcast.         if ($attribute_to_retain) {
          $this->assertNotEmpty($xpath->query("//img[@$attribute_to_retain]"));
        }
      }
    }
  }

  /** * Tests that arbitrary attributes are allowed via GHS. * * @dataProvider providerLinkability */

$this->drupalGet($this->host->toUrl('edit-form'));
    $this->waitForEditor();

    $page->pressButton('Source');
    $editor_dom = $this->getEditorDataAsDom();
    $drupal_media_element = $editor_dom->getElementsByTagName('drupal-media')->item(0);

    // Add `layercake-side` class which is used in `ckeditor5_test_layercake`,     // as well as an arbitrary class to compare behavior between these.     $drupal_media_element->setAttribute('class', 'layercake-side arbitrary-class');
    $textarea = $page->find('css', '.ck-source-editing-area > textarea');
    $textarea->setValue($editor_dom->C14N());
    $page->pressButton('Source');

    // Ensure that the `layercake-side` class is retained.     $this->assertNotEmpty($assert_session->waitForElement('css', '.ck-widget.drupal-media.layercake-side'));

    // Ensure that the `arbitrary-class` class is removed.     $assert_session->elementNotExists('css', '.ck-widget.drupal-media.arbitrary-class');
    $page->pressButton('Save');

    // Check that the 'content has been updated' message status appears to confirm we left the editor.     $assert_session->waitForElementVisible('css', 'messages messages--status');

    

        // bubble up the value of the class attribute of the captioned element,         // this allows it to collaborate with e.g. the filter_align filter.         $tag = $node->tagName;
        $classes = $node->getAttribute('class');
        $node->removeAttribute('class');
        $node = ($node->parentNode->tagName === 'a') ? $node->parentNode : $node;
        $filter_caption = [
          '#theme' => 'filter_caption',
          // We pass the unsanitized string because this is a text format           // filter, and after filtering, we always assume the output is safe.           // @see \Drupal\filter\Element\ProcessedText::preRenderText()           '#node' => FilteredMarkup::create($node->C14N()),
          '#tag' => $tag,
          '#caption' => $caption,
          '#classes' => $classes,
        ];
        $altered_html = \Drupal::service('renderer')->render($filter_caption);

        // Load the altered HTML into a new DOMDocument and retrieve the element.         $updated_nodes = Html::load($altered_html)->getElementsByTagName('body')
          ->item(0)
          ->childNodes;