getMediaImageSourceField example

  protected function applyPerEmbedMediaOverrides(\DOMElement $node, MediaInterface $media) {
    if ($image_field = $this->getMediaImageSourceField($media)) {
      $settings = $media->{$image_field}->getItemDefinition()->getSettings();

      if (!empty($settings['alt_field']) && $node->hasAttribute('alt')) {
        // Allow the display of the image without an alt tag in special cases.         // Since setting the value in the EditorMediaDialog to an empty string         // restores the default value, this allows special cases where the alt         // text should not be set to the default value, but should be         // explicitly empty instead so it can be ignored by assistive         // technologies, such as screen readers.         if ($node->getAttribute('alt') === '""') {
          $node->setAttribute('alt', '');
        }