title: purpose of @ in urls without encoding
body: <p>As I heard</p>
  <blockquote>
  <p>following symbols are reserved and can't be used without encoding in url.<br>
  * ' ( ) ; : @ &amp; = + $ , / ? % # [ ]</p>
  </blockquote>
  <p>What's the real purpose of @without encoding in urls?
  how it can be used?</p>