code: function eachImg(layer, callback) {
        var imgtags = layer._container.children[0].children;
        for (var i in imgtags) {
          if (imgtags[i].tagName === 'IMG') {
            callback(imgtags[i]);
          }
        }
      }
docs: Cribbed from Leaflet https://github.com/Leaflet/Leaflet/blob/master/spec/suites/layer/tile/TileLayerSpec.js#L302-L309