What defines private sites, I wonder – beyond "such as local IP addresses like 192.168.0.1, single-label hostnames, and shortlinks like intranet/"?

Non-unique hostnames, which are RFC 1918 space, single-label hostnames, and addresses assigned to mDNS (.local).

Single label hostnames had an issue where it’s hard to type them into a browser.

How to fix this?

Usually, completing the domain name by adding the final period will do the job. Instead of entering myprinter into the address bar, try myprinter. so your DNS server doesn't try to resolve myprinter, myprinter.domain, myprinter.domain.tld, and whatever other search domains have been configured. A real, fully-qualified domain ends in a period, though most tools will happily let you avoid that final period.

Alternatively, .local domains will work for mDNS-capable devices (and non-mDNS-capable devices if you like to risk things breaking randomly), and the .internal TLD has been reserved so .internal domains should also work for local addresses.

Add a /, e.g. `shortname/`

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