I've had a look at this. The head element is currently not parsed at all, so it ends up inside the document.
There are mechanisms in Sink to handle <meta name="author" .../> and <meta name="date" .../> but not for <meta name="keyword" .../>. So in order for this to work we need to add the methods Sink.keyword() and Sink.keyword_().
That said I haven't succeeded in parsing author and date correctly.
Also, there is no standard set of meta names that are valid. We would have to specify that ourselves in the DTD/XSD. See http://www.w3.org/TR/html401/struct/global.html#h-7.4.4