update doc

Closes #3215627

core/lib/Drupal/Core/Render/Element/HtmlTag.php

@@ -16,8 +16,8 @@
  * - #tag: The tag name to output.
  * - #attributes: (array, optional) HTML attributes to apply to the tag. The
  *   attributes are escaped, see \Drupal\Core\Template\Attribute.
- * - #value: (string, optional) A string containing the textual contents of
- *   the tag.
+ * - #value: (string|MarkupInterface, optional) The textual contents of the tag.
+ *   Strings will be XSS admin filtered.
  * - #noscript: (bool, optional) When set to TRUE, the markup
  *   (including any prefix or suffix) will be wrapped in a <noscript> element.
  *
@@ -29,6 +29,8 @@
  *   '#value' => $this->t('Hello World'),
  * ];
  * @endcode
+ *
+ * @see \Drupal\Component\Utility\Xss::filterAdmin().
  */
 #[RenderElement('html_tag')]
 class HtmlTag extends RenderElementBase {