code: def _find(self, pair, default=None):
          
          from fontTools.ufoLib.kerning import lookupKerningValue
          font = self.font
          groups = font.groups
          return lookupKerningValue(pair, self, groups, fallback=default)
docs: This is the environment implementation of
          :attr:`BaseKerning.find`. This must return an
          :ref:`type-int-float` or `default`.