Warning: this module is experimental and subject to change and even removal at any time.
For background/rationale, see:
* http://www.intertwingly.net/blog/2007/01/08/Xhtml5lib * http://tinyurl.com/ylfj8k (and follow-ups)
References:
* http://googlereader.blogspot.com/2005/12/xml-errors-in-feeds.html * http://wiki.whatwg.org/wiki/HtmlVsXhtml
@@TODO:
Selectively lowercase only XHTML, but not foreign markup