title: what is the # symbol in the url
body: <p>I went to some photo sharing site, so when I click the photo, it direct me to a url like </p>
  
  <p><code>www.example.com/photoshare.php?photoid=1234445</code></p>
  
  <p>. and when I click the other photo in this page the url become </p>
  
  <p><code>www.example.com/photoshare.php?photoid=1234445#3338901</code></p>
  
  <p>and if I click other photos in the same page, the only the number behind # changes. Same as the pretty photo like </p>
  
  <p><code>www.example.com/photoshare.php?album=holiday#!prettyPhoto[gallery2]/2/</code></p>
  
  <p>.I assume they used ajax because the whole page seems not loaded, but the url is changed.</p>