Hopefully this will save you hours of pain... This might be common knowledge, but I was unaware that Nokogiri escapes some text characters when rendering XML!
I was trying to use Nokogiri XML builder to put together an ATOM feed, and spent hours trying to bug fix what I thought was Markdown escaping HTML characters. It turns out that Nokogiri escapes these as well....
Let's cut to the chase. Here's what you need to do to force Nokogiri to render raw XML (no escaping).
xml.content(:type => "html") do xml << html # Have to do it this way to prevent autoescaping end