Should be (perhaps) up to 27 defined levels, tbd (currently 19). Also, coordinate number with [polyfill](https://github.com/Maps4HTML/Web-Map-Custom-Element/blob/2677ab548430ce597269fc5e3455052e5da5993a/src/mapml/index.js#L638) https://maps4html.org/MapML/spec/#OSMTILE
Should be (perhaps) up to 27 defined levels, tbd (currently 19). Also, coordinate number with polyfill
https://maps4html.org/MapML/spec/#OSMTILE