title: how to make a custom atributte w3 valid?
body: <p>I have the following code that is used to open a menu over the account anchor:</p>
  
  <pre><code>echo "&lt;li&gt;&lt;a href='./account/' data-flexmenu='account'&gt;Account"&lt;/a&gt;&lt;/li&gt;";
  </code></pre>
  
  <p>the <code>data-flexmenu='account'</code> inform what menu should be shown, in that case, the account menu.</p>
  
  <p>The problem is that im getting error on w3 validator: <code>there is no attribute "data-flexmenu"</code></p>
  
  <p>Is there a way to make that valid?</p>