code: private void checkAsCss(InputSource is) throws IOException, SAXException {
          String charset = "UTF-8";
          if (is.getEncoding() != null) {
              charset = is.getEncoding();
          }
          List<InputStream> streamsList = new ArrayList<>();
          streamsList.add(new ByteArrayInputStream(CSS_CHECKING_PROLOG));
          streamsList.add(is.getByteStream());
          streamsList.add(new ByteArrayInputStream(CSS_CHECKING_EPILOG));
          Enumeration<InputStream> streams = Collections.enumeration(streamsList);
          is.setByteStream(new SequenceInputStream(streams));
          is.setEncoding(charset);
          sourceCode.setIsCss();
          sourceCode.initialize(is);
          try {
              htmlReader.parse(is);
          } catch (SAXParseException e) {
          }
      }
docs: /* *
  Packs a CSS document into an HTML wrapper and validates it.