PUBLIC MARKS with tags tabindex & accessibility

An increasing number of web applications are using JavaScript to mimic desktop widgets like menus, tree views, rich text fields, and tab panels. Web developers are constantly innovating, and future applications will contain complex, interactive elements such as spreadsheets, calendars, organizational charts, and beyond. Until now, web developers wanting to make their styled <div> and <span> based widgets keyboard accessible have lacked the proper techniques. However, keyboard accessibility is part of the minimum accessibility requirements that any web developer should be aware of.

the usage of tabindex and focus