[Feature suggestion] Enable umap to embed more than one dynamic (tiled) background map

[Wikinaut]

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Situation:

I use umap with a self-defined, tiled background map for a certain area, and of course several annotation layers.

User needs:

I wish to overlay (or underlay) this first background map (my own tiles from my server) with a certain opacity (let's say, 50%) with a second background map like public OSM-DE.

Currently, I do not see a mechanism or method how this could be achieved directly, and live, using umap.

See also https://twitter.com/Wikinaut/status/1480307131177918467?s=20

Circumvention, ad-hoc solution:

An ad-hoc solution would be to define a kind of "proxy map server", another server, who merges tiles from the first and the second background maps, however this is not target of my issue report.

Feature suggestion/request:

Enable umap to embed, to render more than one dynamic background map.