w3C compliance

The role="button" attribute is required for accessibility. It is used to indicate to screen readers that a non-button element (e.g. an <h2>) should be treated as a button.

You can read more about its usage on MDN.

Thank you for your answer. I understand why you use the role attribute but that generates some mistakes in the validator.w3.org :

Error: Bad value button for attribute role on element h2.

and some warning with button :

Warning: The button role is unnecessary for element button.

I’m aware of the validator error. However, at this point I am prioritizing accessibility over ensuing no validator warnings or errors. If you absolutely must have no validator errors, this may not be the right plugin for you.