"If it's a hostname it has to correspond to a valid domain name, right?" If it is listed in the ICANN DNS, maybe. DNS is not mandatory for a website to work.

"If it's a hostname it has to correspond to a valid domain name, right?" If it is listed in the ICANN DNS, maybe. DNS is not mandatory for a website to work. Most of the time I do not use DNS when reading the www. I have my own databases of the info I need to reach websites. Not that I expect anyone else would do this, but it is very fast and reliable.