Fieldsets in Plone z3c.form

One day, my task is adding fielsets in z3c.form on Plone site. Most of the examples in Internet are showing the form field interface class is inherited from model.Schema in plone.supermodel. Unfortunately, in my case, the class is inherited from Interface in zope.interface. Luckily, fieldsets mentions z3c.form.group could do the jobs. It solved my problem.