code: def _duplicateLayer(self, layerName, newLayerName):
          
          newLayer = self.getLayer(layerName).copy()
          return self.insertLayer(newLayer, newLayerName)
docs: This is the environment implementation of :meth:`BaseFont.duplicateLayer`.
          **layerName** will be a :ref:`type-string` representing a valid layer name.
          The value will have been normalized with :func:`normalizers.normalizeLayerName`
          and **layerName** will be a layer that exists in the font. **newLayerName**
          will be a :ref:`type-string` representing a valid layer name. The value will
          have been normalized with :func:`normalizers.normalizeLayerName` and
          **newLayerName** will have been tested to make sure that no layer with
          the same name exists in the font. This must return an instance of a
          :class:`BaseLayer` subclass.
  
          Subclasses may override this method.