public static @Nullable String getDtdUri(XmlDoctype doctype) {
    if (doctype != null) {
      String docType = doctype.getDtdUri();
      if (docType == null) {
        final String publicId = doctype.getPublicId();
        if (PsiTreeUtil.getParentOfType(doctype, XmlDocument.class) instanceof HtmlDocumentImpl &&
            publicId != null && publicId.contains("-//W3C//DTD ")) {
          return guessDtdByPublicId(publicId);
        }
        else if (HtmlUtil.isHtml5Doctype(doctype)) {
          docType = doctype.getLanguage() instanceof HTMLLanguage
                    ? Html5SchemaProvider.getHtml5SchemaLocation()
                    : Html5SchemaProvider.getXhtml5SchemaLocation();
        }
      }
      return docType;
    }
    return null;
  }
public static @Nullable String getDtdUri(XmlDoctype doctype)