What's the difference between tabindex="false" and empty tabindex?

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~

Solution

There is no difference.

As Xufox explains in a comment, tabindex can only have integers as values. This is indicated in the HTML specification:

The tabindex attribute, if specified, must have a value that is a valid integer.

Having tabindex (without a value), or tabindex="false" or tabindex=false is irrelevant as all of them will fail the rules for parsing integers (in steps 5, 7, and 7 respectively). In those cases, browsers will ignore the value and apply the logic that they apply by default to any element.

So all of the following would be treated equally:

<input tabindex="false" />
<input tabindex=false />
<input tabindex="" />
<input tabindex />
<input />