Validation error

https://validator.w3.org/ shows an error on button elements

Bad value button for attribute role on element li.

This is the code reported:

<li data-wvstooltip="XS" class="variable-item button-variable-item button-variable-item-xs selected" title="XS" data-value="xs" role="button" tabindex="0">

Everything is working perfect only that for those people trying to validate their sites it will throw that error.