title: how to strip all characters except for alphanumeric and underscore and dash?
body: <p>I'm not an expert with regex:(
  I'm trying to to strip all characters from the string except for alpanumeric and underscore and dash.
  Is this the correct syntax?:</p>
  
  <pre><code>preg_replace("/[^a-z0-9_-]+/i", "", $string);
  </code></pre>