Agreed. I love me all the Unicodes, all the time! For typing, for display, for whatever internal app logic, variable names, the names of children etc. The IRI

Agreed. I love me all the Unicodes, all the time! For typing, for display, for whatever internal app logic, variable names, the names of children etc. The IRI RFC does however specify that for transmission/interchange the IRIs need to be percent-encoded to form valid URIs. That's pretty straightforward! A good user agent will fully transcode whatever characters I type in the address bar, generating a valid IRI. A bad user agent will complain and say that whatever it was I typed was very nice but not a valid interweb, and I have a bad day. A broken user agent may generate some broken encoding (or just pass on whatever I typed in UTF-8 or CP-1252), and some web admins may have a bad day, if they weren't already. But the location bar is not the only place that URLs come from (less and less every day). When a web application (e.g. 301 redirect) or a resource (e.g. external document reference) uses an RFC-3987 noncompliant identifier, just how far should the user-agent bend over backwards to fetch the resource? Some browsers seem to do a lot, but it's not clearly documented just how much (see elsewhere in the comments), and among the article's laments was the observation that when any browser accepts dodgy identifiers, it places a burden on everyone else to accept the same. Seems that WHATWG hopes to formally codify just how dodgy you can get away with without the identifier being "too dodgy", but I get the impression that this will be an expansive definition ("hey, if they did it, you can do it! we believe in you"). This is an understandable approach, as they are trying to document the state of the web, but it does put extra burden onto anyone dealing methodically with URLs henceforth, rather than being strict and drawing some clear boundaries up for people constructing URLs. I'm expecting to see a lot of "SHOULD" and not a lot of "MUST NOT" :-/