It excludes all html tags and attributes except for those that are
whitelisted using the same lists as used by Mark Pilgrim's Universal Feed
-Parser, documented at <http://feedparser.org/docs/html-sanitization.html>.
+Parser, documented at <http://feedparser.org/docs/html-sanitization.html>
+(dead link 2011.10.31).
Notably it strips `style` and `link` tags, and the `style` attribute.
All attributes that can be used to specify an url are checked to make sure