title: HTML5 input validate letters and numbers
body: <p>I need a pattern for a HTML5 form.</p>
  
  <ul>
  <li>Lowercase letters accepted</li>
  <li>Uppercase letters accepted</li>
  <li>Numbers accepted</li>
  <li>Minus character accepted</li>
  </ul>
  
  <p><strong>HTML so far</strong></p>
  
  <pre><code>&lt;input type="text" pattern="[a-zA-Z0-9-]" required&gt;
  </code></pre>
  
  <p>The code above does not work. I guess I'm close?</p>