Standardizing on IDNA 2003 in the URL Standard
Shawn.Steele at microsoft.com
Fri Aug 23 21:25:40 CEST 2013
> 2. The TR46 deviation character
> support can be dropped in clients once the major registries
> that allow them provide a bundle or block approach to labels that
> include them, so that new clients can be
> guaranteed that URLs won't go to a different location than
> they would under IDNA2003. The bundle/block needs to last
> while there are a significant number of IDNA2003 clients
> out in the world. Because newer browsers have automatic
> updates, this can be far faster than it would have been a
> few years ago.
That's not necessarily true. If someone's subdomain uses some IDNA2003 domain name that lands on a different machine, the client applications will get the bug reports that they broke the customer when a customer's URL stops working. Blocking at the registry could have a similar issue (if the user wants to move from one to another). Also we cannot enforce that the registrars bundle-or-block.
However if the registrars DO bundle the names with the IDNA2003 form (other variations could be blocked), and the client software continues to resolve using the transient rules for these 5 characters, the user will always land on the right machine, no matter which way they enter the name. The "worst" problem could be that the address bar looks a little different than what the user entered. Which could be considered a UI problem. And if the clients really thought that UI issue was worth fixing, they could ensure that they didn't map the form the users entered for these few characters.
More information about the Idna-update