title: How do I validate XHTML, ATOM, and CSS in Ruby?
body: <p>I'd like to run validations on the static web content I'm creating.  Are there any good validators for XHTML, ATOM, and CSS?  (The first two would be covered by any general-purpose XML-DTD validator.)</p>
  
  <p><strong>Later</strong></p>
  
  <p>I failed to specify that I wanted <em>local</em> validation, not something that uses the W3C service.</p>