Hi Tourism_info,

Here, indoor=yes means a feature is inside.
This us not related to indoor tagging scheme, that tries to described rooms and corridors etc.

Or (just kidding) do you want to retag all defibrillators with indoor=yes to indoor=defibrillator?
https://wiki.openstreetmap.org/wiki/Tag:emergency%3Ddefibrillator

In this context, indoor=yes is a synonym to location=indoor
https://wiki.openstreetmap.org/wiki/Tag:location%3Dindoor

I hopefully this helps to get the subtle difference the indoor tag can be used for.

Best regards
Metzor

