docs: def accessor(self):
          """Get an attribute's accessor with the getter and the setter.
  
          :return: `Accessor` instance.
          """
          if isinstance(self.attr, Accessor):
              return self.attr
  
          if callable(self.attr):
              return Accessor(getter=self.attr)
  
          attr = self.attr or self.name
          return Accessor(getter=attr, setter=attr)