I was working on re-building a custom select list component to make it more keyboard-friendly when I encountered a strange bug: the <section> element wrapping the result elements was in the focus order, even though it didn't have tabIndex set on it. Since my custom component handles focus traversal on the result items on its own, this extra tab stop was a bug.

After some digging, I discovered that the culprit was a CSS class setting overflow: scroll on the section. With overflow: scroll set on an element, both Firefox and Chrome1 put the element in tab order, as an accessibility feature. With the element in tab order, users can use the arrow keys to scroll through the scrollable area.

Why do browsers do that?

If the scroll-containing element wasn't in tab order, there would be no way for a keyboard-only user to scroll and see all the content.

Interested in digging more? Read the initial bug report and fix documentation at the Chromium bug tracker.

What if I don't want this behavior?

In my case, since I was implementing focus traversal through the scrollable list myself, it didn't make sense for the container element to receive keyboard focus. So, I set tabindex='-1' on the container section, which the browsers I tested respected (that is, the section element was no longer in keyboard tab order).

If you're not providing an alternate means for keyboard-only users to scroll through a scrollable element, leave this behavior alone. It's making your site more accessible, without you having to do anything special - how neat is that??

Test it yourself

1. And possibly other browsers; those are the only two I tested. Safari seems not to do this.