the element represents an element that is is focusable (that is, that you can click or navigate with tab or an element which is part of the sequence of focusable elements in the document),
the relative order of the element in the sequence of focusable elements known as tab order in the document
Sequential keyboard navigation
Remove
You can remove an element from the tab order by setting tabindex=“-1”
Add
You can add an element to the tab order by setting tabindex=“0”: