impossible to display levels 19 and 20 of an overlay tile layer

[Kernonen]

In the chapter Overlay cell, I added as stated link to a overlay tile map. Display is fine from levels 15 to 18 but impossible to have levels 19 to 20 displayed.
I changed maxZoom values in line 86 to
L.tileLayer.provider(basemap, {maxZoom: 20}
but no effect. Is there another place where max Zoom for overlays are specified ?

Also, I did install a slider on the map to change overlay opacity but It doesn't work (console says : ReferenceError: Can't find variable: overlay)
Here's slider in html :

[ilyankou]

Hi @Kernonen

According to Leaflet documentation, "If not specified and at least one GridLayer or TileLayer is in the map, the highest of their maxZoom options will be used instead." It is likely the case that the basemap you selected is only available for zoom levels up to 18. Consider changing to a more detailed tile layer.