code: public static boolean isValidCSS (@Nonnull @WillClose final Reader aReader, @Nonnull final ECSSVersion eVersion)
    {
      ValueEnforcer.notNull (aReader, "Reader");
      ValueEnforcer.notNull (eVersion, "Version");
  
      try
      {
        final CSSCharStream aCharStream = new CSSCharStream (aReader);
        final CSSNode aNode = _readStyleSheet (aCharStream,
                                               eVersion,
                                               getDefaultParseErrorHandler (),
                                               new DoNothingCSSParseExceptionCallback (),
                                               false);
        return aNode != null;
      }
      finally
      {
        StreamHelper.close (aReader);
      }
    }
docs: Check if the passed reader can be resembled to valid CSS content. This is
  accomplished by fully parsing the CSS each time the method is called. This
  is similar to calling
  {@link #readFromStream(IHasInputStream, Charset, ECSSVersion)} and checking
  for a non-<code>null</code> result.
  
  @param aReader
  The reader to use. May not be <code>null</code>.
  @param eVersion
  The CSS version to use. May not be <code>null</code>.
  @return <code>true</code> if the CSS is valid according to the version,
  <code>false</code> if not