pp. The
<code>/photos</code> route will render the <code>photos</code> template with the list of
photos as the model, which never changes. But when the user clicks on a
particular photo, we want to display that model with the <code>photo</code>
template. If the user goes back and clicks on a different photo, we want
to display the <code>photo</code> template again, this time with a different model.</p>
<p>In cases like this, it's important that we include some information in
the URL about not only which tem