code: def unconstrain_fixed(self):
          
          unconstrained = self.unconstrain(__fixed__)
          self._highest_parent_._set_unfixed(self, unconstrained)
          #if self._default_constraint_ is not None:
          #    return self.constrain(self._default_constraint_)
          return unconstrained
docs: This parameter will no longer be fixed.
  
          If there was a constraint on this parameter when fixing it,
          it will be constraint with that previous constraint.