How perplexing that it works at all! I want to know how that works.

It’s just a TLD that actually resolves; Most don’t. For example, http://com./ doesn’t resolve even though it has “subdomains”.

This does though beg the question: can a second level domain (root website) have (what we call) subdomains and not resolve itself? For example, example.example.com would resolve, but example.com wouldn’t?

Thanks for the clarification. I see, so an owner can choose to resolve the top-level domain by itself, I didn't know that.

When I visit "com.", indeed it doesn't resolve and the browser falls back to "www.com" (which exists).

That makes me wonder, if I wanted a TLD by itself to resolve to my own site, is it even feasible for a "regular person"?

What's served on "http://pn/" looks like someone's experiment, but I guess they must own the TLD (or have connections to the owner)..?

Should be easy to set up, especially if you have your own authoritative DNS server. Just don't publish an A record for your main domain.

Yes, this is quite common.

Yeah, how does that work?

I'd guess it's the TLD of the Pitcairn Islands set to resolve to this random page. For example

    http://ca. 

resolves to the Canadian domain registrar.

Not necessarily a random page, but an “it works” page so you know your server works.