Ahoj,

I miss a complete documentation of all the options the KDE Marble's map definition `.dgml`-files can take and what they do.

Currently, I always have to resort on trying to infer from already created maps, but that probably results in not good custom `.dgml` files (see e.g. https://gitlab.com/dreieckli/marble-maps-extra, https://gitlab.com/marble-restricted-maps/virtualearth, https://aur.archlinux.org/packages/marble-maps-sachsen, https://gitlab.com/dreieckli/marble-maps-thunderforest). Specifically, I want to make a hillshading-only map from the tiles at http://osmscout.karry.cz/hillshade/ (see https://gitlab.com/dreieckli/marble-maps-extra/-/tree/main/maps/earth/hillshading-karry for .dgml file), but I fail since the tiles are only alpha(?) overlays and I not yet found out a way how to blend them on a background. Also, I could not change the empty map background even with setting `<map bgcolor="#cccccc">` or something else -- it stays black.

I am very confused what is possible with `.dgml`-files and how to set map background -- so I request a documentation for people who want to provide maps for KDE marble.

I think if this is easier, more maps would be publicly provided, which in turn could make KDE marble more popular.

Regards!