[salex89]

I'm also not sure, and interested. Sometimes modules fit together, sometimes not. However, there are nicer examples of this concept. My personal favorite, with an online switch configurator: https://www.tem-si.com/

I love this setups because you can easily retrofit a switch with a motion sensor, not needing to drill new holes or add cables.

[OJFord]

Yes, I struggled to know what to link really - ideally it would be the spec, if only I knew there was one and where to find it! No Wikipedia page on them even.

I've upvoted someone's question on a StackExchange site in the past asking for a standard, and I think accidentally opened a duplicate a year later or something myself:

https://diy.stackexchange.com/questions/177403/euro-modules-...

Anyway, I ended up with this link just because I thought it made the modular concept quite clear; not endorsing theirs specifically. My faceplates and modules are from different manufacturers, many of the modules unmarked generics.

[pulse7]

I have those in my house. They are modular (see https://www.tem-si.com/design-switches/).