Changing the xn-- prefix

Shawn Steele Shawn.Steele at
Thu Mar 20 19:18:31 CET 2008

I think that changing the prefix would be a really bad idea:

* Changing the domain name would break existing comparisons that rely on the punycode.  (domain name xn--A wouldn't necessarily equal domain name xx--A)

* names wouldn't match in the registry either.  The browser would have to try the new prefix name, then if that failed, it'd have to try the xn-- name for back compat.

* What happens when the xn-- and the new prefix names for the same machine/Unicode name point to different servers?  This could happen either because the registrars messed up or they are on a subnet that didn't know better?

* Developers would have to consider 2 versions for even simple applications.

I think that these are much more serious that changing behavior for anything that is considered "bad" (for security) today.  If a "bad" domain stops working we probably want it to stop working.

Our intent is to replace the IDN resolution mechanism for IE/Windows/.Net with updated tables when they become available.  We would oppose anything that causes us to have multiple revisions or complex code paths for edge cases.

- Shawn

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