code: def link_zscale(st):
      
      # FIXME should be made more generic to other parameters and categories
      psf = st.get('psf')
      psf.param_dict['zscale'] = psf.param_dict['psf-zscale']
      psf.params[psf.params.index('psf-zscale')] = 'zscale'
      psf.global_zscale = True
      psf.param_dict.pop('psf-zscale')
      st.trigger_parameter_change()
      st.reset()
docs: Links the state ``st`` psf zscale with the global zscale