title: How to write regular expression to match only numbers, letters and dashes?
body: <p>I need an expression that will only accept:  </p>
  
  <ul>
  <li>numbers  </li>
  <li>normal letters (no special characters)  </li>
  <li>-</li>
  </ul>
  
  <p>Spaces are not allowed either.</p>
  
  <p>Example:
  The regular expression should match:<br>
  <code>this-is-quite-alright</code></p>
  
  <p>It should not match<br>
  <code>this -is/not,soålright</code></p>