title: HAML table row class
body: <p>I'd like to add a class to the table row like so:</p>
  
  <pre><code>  %tbody
      - @article.each do |x|
       %tr [add class here]
         %td= check_box_tag "check-box"
         %td= x.short_title
         %td= x.label.nil? ? '' : x.label.title
         %td= published_at(x)
         %td= last_update(x)
  </code></pre>
  
  <p>however when I try to I get the error: </p>
  
  <p>Illegal nesting: content can't be both given on the same line as %tr and nested within it.</p>