Is tabindex hack for CSS :focus specified somewhere?

Question

There is a hack to make work :focus pseudoclass for div elements: adding to div tabindex. Like this:

.testFocus:focus{
    background: red;
}

<div class="testFocus" tabindex="0">awesomeDiv</div>

Is this behavior specified somewhere in W3C documents (where?) or is it just a non-documented hack?

"This behavior" consists of:

1. div element is not focusable by default.
2. div element with tabindex is focusable.

Answer 1

tabindex is one of the global attributes. This means it can be specified on all HTML elements.

0 is a valid value (see "If the value is a zero" under the definition of tabindex).

So your HTML is fine.