John Stracke writes: > For that matter, a well-designed application will not even make it > possible to enter anything but ASCII in an input field (whatever) for a > domain name. That's incredibly bad design. You're violating the basic principles of information hiding articulated by Parnas in the early 1970s. Instead of isolating the name-existence decision in one place (the DNS server's database), you're spreading the decision across a huge number of programs on a huge number of machines. Changing a decision becomes extremely expensive. We're seeing the economic consequences of this in BIND's res library. That library is the most widely used UNIX DNS-lookup mechanism, and is one of the largest sources of UTF-8 failures; see http://pi.cr.yp.to. It has to be fixed on a huge number of machines. (Note that this cost, together with the other costs of making UTF-8 IDNs work, is only a tiny fraction of the costs of making IDNA work.) If you think that the 8-bit problems in res are an example of people agreeing with your design ideas, you're mistaken. The change was made in a panic in 1996, when CERT announced that several programs had security flaws based on careless use of DNS PTR results. Of course, anyone who thinks about the problem for a moment can see that unusual DNS A _input_ has no relevance to the security issue, but people in a security-related panic often don't stop to think about the damage they're causing. > Basic rule of usability: making user mistakes impossible is > better than catching them after the fact. You obviously aren't achieving that goal. You're catching typos if and only if they involve non-ASCII characters. What about ASCII typos? What is the basis for your assertion that the no-such-name message should, as a matter of UI design, be different between these two situations? Even worse, what about ASCII typos that produce valid domain names? Basic rule of usability: Have the computer copy the data so that the user doesn't have an opportunity to make a mistake. Saves time, too. ---D. J. Bernstein, Associate Professor, Department of Mathematics, Statistics, and Computer Science, University of Illinois at Chicago