title: Magento->filter product visibility in collection
body: <p>We use this Magento code to get a list of publications to pick 2 from to show in a Bookstore section.</p>
  
  <pre><code>$collection = Mage::getModel('catalog/category')-&gt;getCollection();
  $collection-&gt;addAttributeToSelect('url_key')
      -&gt;addAttributeToSelect('name')
      -&gt;addAttributeToSelect('id')
      -&gt;addAttributeToSelect('description')
      -&gt;addAttributeToSelect('is_anchor')
      -&gt;addAttributeToFilter('is_active', 1)
      -&gt;joinUrlRewrite()
      -&gt;load();
  </code></pre>
  
  <p>How can I add an attribute to select to make it not include the publications that are set 
  to "Not show individually"?</p>
  
  <p>If I add this:</p>
  
  <pre><code>-&gt;addAttributeToFilter('visibility', 4) // Only catalog, search visiblity
  </code></pre>
  
  <p>The code fails with message 'Invalid attribute name: visiblity'</p>