title: What's the difference between tabindex="false" and empty tabindex?
body: <p>As per the title, what is the difference when I have <code>tabIndex="false"</code> versus having empty <code>tabIndex</code>? As a bonus, what's the difference with having <code>tabIndex="false"</code> versus <code>tabIndex=false</code> versus empty <code>tabIndex</code>? </p>
  
  <p>For example: 
  <code>&lt;a tabIndex="false" /&gt;</code> versus <code>&lt;a tabIndex /&gt;</code> versus <code>&lt;a tabIndex=false /&gt;</code></p>
  
  <p>I haven't been able to find any resource or stackoverflow question that sheds light on this scenario. </p>
  
  <p>Thanks in advance~</p>