The decimal has a very specific meaning in host names. That’s not the binding author, that’s how host names work. Each computer has a “fully qualified domain name”. Everything after the first . is considered the host name. Everything after is the domain name. So RA.Nyholm means hostname “RA” and domain “Nyholm”. Therefore, you can’t have a . in a hostname, only in a FQDN. And if you’ve not set up your network to have a FQDN you can’t use a . at all.
That’s why, as Russ explains, iOS replaces invalid characters with -. And further reading the thread Wolfgang posted it appears that once again this is a place where Apple when their own way and had to go though all sorts of complications to interoperate with the rest of the world.
But all of this is outside of openHAB. openHAB can do a lot but it’s not going to teach you the basics of the technology you are trying to interact with. We simply do not have enough people nor expertise here to document the basics for all the technologies that OH can interact with. So I don’t think documenting how hostnames work in general belong in openHAB’s documentation. Maybe a link to the RFC that defines the way that hostnames work might be appropriate. Or a link to the thread Wolfgang posted with a warning about how Apple “goes their own way.”
The OH docs come from lots of different repos and therefore who reviews it will largely depend on what is being changed. If it’s part of the core docs or developer docs, one of the openhab-docs maintainers will review it. If it’s docs for a binding, usually the binding author or one of the openhab-addons maintainers. There are more sources for various parts of the docs and a good post about that is at [Wiki] How to contribute to the openHAB Documentation.
But the key takeaway is nothing gets added to the docs without at least one person reviewing it for correctness and conformity to style and such. So don’t worry about mucking up the docs. We definitely need the help.