class FieldFilteredMarkup

final class FieldFilteredMarkup implements MarkupInterface, \Countable {
    use MarkupTrait;
    
    /**
     * Overrides \Drupal\Component\Render\MarkupTrait::create().
     *
     * @return string|\Drupal\Component\Render\MarkupInterface
     *   A safe string filtered with the allowed tag list and normalized.
     *
     * @see \Drupal\Core\Field\FieldFilteredMarkup::allowedTags()
     * @see \Drupal\Component\Utility\Xss::filter()
     * @see \Drupal\Component\Utility\Html::normalize()
     */
    public static function create($string) {
        $string = (string) $string;
        if ($string === '') {
            return '';
        }
        $safe_string = new static();
        // All known XSS vectors are filtered out by
        // \Drupal\Component\Utility\Xss::filter(), all tags in the markup are
        // allowed intentionally by the trait, and no danger is added in by
        // \Drupal\Component\Utility\Html::normalize(). Since the normalized value
        // is essentially the same markup, designate this string as safe as well.
        // This method is an internal part of field sanitization, so the resultant,
        // sanitized string should be printable as is.
        $safe_string->string = Html::normalize(Xss::filter($string, static::allowedTags()));
        return $safe_string;
    }
    
    /**
     * Returns the allowed tag list.
     *
     * @return string[]
     *   A list of allowed tags.
     */
    public static function allowedTags() {
        return [
            'a',
            'b',
            'big',
            'code',
            'del',
            'em',
            'i',
            'ins',
            'pre',
            'q',
            'small',
            'span',
            'strong',
            'sub',
            'sup',
            'tt',
            'ol',
            'ul',
            'li',
            'p',
            'br',
            'img',
        ];
    }
    
    /**
     * Returns a human-readable list of allowed tags for display in help texts.
     *
     * @return string
     *   A human-readable list of allowed tags for display in help texts.
     */
    public static function displayAllowedTags() {
        return '<' . implode('> <', static::allowedTags()) . '>';
    }

}