Using the tabindex attribute | The Paciello Group – Your Accessibility Partner (WCAG 2.0/508 audits, VPAT, usability and accessible user experience)
▻http://www.paciellogroup.com/blog/2014/08/using-the-tabindex-attribute
The HTML tabindex attribute is used to manage keyboard focus. Used wisely, it can effectively handle focus within web widgets. Used unwisely however, the tabindex attribute can destroy the usability of web content for keyboard users.
The tabindex attribute indicates that an element can be focused on, and determines how that focus is handled. It takes an integer (whole number) as a value, and the resulting keyboard interaction varies depending on whether the integer is positive, negative or 0.