def create_mod_site(self, mc):
        """Create modification site for the BaseAgent from a ModCondition."""
        site_name = get_mod_site_name(mc)
        (unmod_site_state, mod_site_state) = states[mc.mod_type]
        self.create_site(site_name, (unmod_site_state, mod_site_state))
        site_anns = [Annotation((site_name, mod_site_state), mc.mod_type,
                                'is_modification')]
        if mc.residue:
            site_anns.append(Annotation(site_name, mc.residue, 'is_residue'))
        if mc.position:
            site_anns.append(Annotation(site_name, mc.position, 'is_position'))
        self.site_annotations += site_anns
Create modification site for the BaseAgent from a ModCondition.