 Why is this important?

A keyboard-focusable (tabbable) element has been found with an invalid role.
When users reach elements by tabbing with the keyboard, 
the element's role provides context about the expected interaction, 
and assistive technologies like screen readers can provide additional information about ways to interact. 
The only elements that should be in the tab order should be operable widgets. 
Inoperable elements, such as headings, can be given focus by developers; however, they should not 