title: My Vim replace with a regex is throwing a `E488: Trailing characters`
body: <p>I'm trying to find all instances of a Twitter handle, and wrap an anchor tag around them.</p>
  
  <pre><code>:%s/\(@[\w]\)/&lt;a href="http://www.twitter.com/\1"&gt;\1&lt;\/a&gt;/gc
  </code></pre>
  
  <p>Which gives me: </p>
  
  <pre><code>E488: Trailing characters
  </code></pre>