title: DOM error while using .classList.add method
body: <p>So when I'm trying to add two classes to my elemeny by this code</p>
  <p>I have this error</p>
  <pre><code>Uncaught DOMException: Failed to execute 'add' on 'DOMTokenList': The token provided ('1 cell-red') contains HTML space characters, which are not valid in tokens.
  </code></pre>
  <p>I don't see any incorrect white space in here</p>