Builder::XmlMarkup should escape "quotes" in attributes, right?

Railsers:

What's with Builder::XmlMarkup doesn't escape double quotes in tag attributes? Ogle:

  def test_xml_markup     x = Builder::XmlMarkup.new     x.span :id => 'I be a "quoted" string'     assert_not_equal '<span id="I be a "quoted" string"/>', x.target!   end

That fails its assertion, and would also fail a check for well-formed XML.

I was relying on XmlMarkup to detect _how_ to mark quotes up, so I wouldn't need to research it myself. &quot; is supported everywhere, right? I'm going to need to get arbitrarily nested here (using the XmlMarkup to build XHTML-style HTML that transports arbitrarily complex strings), so I need perfectly balanced escapes and de-escapes here.