This is not always true as it’s a feature of the specific router and not part of the spec. To be fair, it’s a feature that’s now fairly common because of how handy it is.

Additionally; many flavours and types of operating systems transparently handle local discovery and resolution just not all of them.

For anyone looking to test this, open a terminal and ping the short domain. In the response it will show what domain it actually used. In my case ‘ping proxmox’ shows ‘proxmox.<my personal domain>.com’.

This is entirely pedantic but I think interesting if you have a mind for optimizing: The discovery/search does introduce some delay.