In reply to mark k..

@mark The Text tab of the TinyMCE Text widget allows the same HTML as you can put in post content. The new Custom HTML widget coming in 4.8.1 will allow all of the HTML that was previously allowed in the Text widget as well. In all cases, however, the ability to put absolutely any HTML has always been restricted based on whether or not the user has the unfiltered_html capability. Admin users on multisite installs (who are not superadmins) for example cannot put script tags in post content or text widgets. Nothing is changing here.