I didn’t find anything about using a decimal point or comma (e.g. for width of a way). Or is this dependent on the country you are in?
It isn’t said in so many words, but it seems the decimal point is the way to go.
Decimal point is consensus in documentation and most discussions (even though it’s only made explicit by examples), but in practice you will find both. Probably because most people don’t read documentation and editor presets don’t care at all.
You are right, not reading a documentation is very common. But after searching the wiki for some time without success, I just decided to ask. Finding something so specific in the wiki is quite impossible…