title: What does the less than sign (<) for class mean?
body: <p>Following code is from Ruby on Rails.</p>
  
  <pre><code>  ...some code here...
  
    unless ActionController::Base &lt; ActionController::Testing
      ActionController::Base.class_eval do
        include ActionController::Testing
      end
    end
  
    ... some code here...
  </code></pre>
  
  <p>What does <code>ActionController::Base &lt; ActionController::Testing</code> mean in this context?</p>