title: What can a Canvas app do that an external site using Facebook's SDK cannot?
body: <p>I've read <a href="https://developers.facebook.com/docs/guides/canvas/">Facebook's documentation for Canvas apps</a> several times, but I'm having a hard time telling which features are available only to Canvas apps and which features are also available to non-Facebook websites that use the JavaScript SDK.</p>
  
  <p>For example, the Canvas documentation mentions Bookmarks, Search, and publishing to the News Feed via the Feed Dialog and Graph API. But you can get all of that on a non-Facebook website, without being a Canvas app, by using the Facebook Login API and Feed Dialog API.</p>
  
  <p>So, what exactly <em>are</em> the features of Canvas? What can a Canvas app do that an ordinary website can't?</p>