As per the title, what is the difference when I have tabIndex="false" versus having empty tabIndex? As a bonus, what's the difference with having tabIndex="false" versus tabIndex=false versus empty tabIndex?

For example:
<a tabIndex="false" /> versus <a tabIndex /> versus <a tabIndex=false />

I haven't been able to find any resource or stackoverflow question that sheds light on this scenario.

Thanks in advance~