While I was looking in Developer console, for a JavaScript App which was consuming a Tiled Map Service, I saw that it was making calls to an URL like:

https://services.arcgisonline.com/ArcGIS/rest/services/Reference/World_Boundaries_and_Places/MapServer/tilemap/4/8/8/8/8

When I tried to figure out what this is, the only place where I found some information, is in this Github Ticket: https://github.com/Esri/esri-leaflet/issues/240

According to this comment, this rest end point tells the JSAPI where there are tiles and where there are not.

That comment was back in 2014. Is any public Documentation available on this REST Endpoint?