In nu.validator.htmlparser version 1.2.0, setting "immutable" features to the supported value throws exceptions.

I've tried using htmlparser with Saxon XSLT processor as follows:
...
XMLReader htmlParser = new HtmlParser(ALTER_INFOSET);
transformer.transform(new SAXSource(htmlParser, new InputSource(input)), 
                      new StreamResult(output));
but I've got:

org.specs.runner.UserError: net.sf.saxon.trans.XPathException: The SAX2 parser nu.validator.htmlparser.sax.HtmlParser does not recognize the 'namespaces' feature
	at net.sf.saxon.event.Sender.configureParser(Sender.java:509)
	at net.sf.saxon.event.Sender.sendSAXSource(Sender.java:304)
	at net.sf.saxon.event.Sender.send(Sender.java:193)
	at net.sf.saxon.event.Sender.send(Sender.java:50)
	at net.sf.saxon.Controller.transform(Controller.java:1611)

because Saxon tries to configure the XML parser like this:
// user-supplied parser: ensure that it meets the namespace requirements
parser.setFeature("http://xml.org/sax/features/namespaces", true);
parser.setFeature("http://xml.org/sax/features/namespace-prefixes", false);

I believe the current implementation is in violation of method's contract as specified in Javadoc for org.xml.sax.XMLReader.setFeature:
...
All XMLReaders are required to support setting http://xml.org/sax/features/namespaces to true and http://xml.org/sax/features/namespace-prefixes to false.