transform td role to td class in HTML-output

Hi everyone, I'm using the DocBook XSL to transform DocBook XML to EPUB and HTML. I would like to transform

td role="breedte-50"

to

td class="breedte-50"

in my HTML output, but unfortunately the output is

td

I have tried to use match:
docbook:td[@role = 'bron']

and I've tried the class.value mode. They both don't work.

I've read two posts (from 2010 and 2011) that address this topic. Is there a way to add classes to td's?

Thanks in advance,
Kind regards,
Michel