RFC 3696: Application Techniques for Checking and Transformation of Names

[pne]

Ever had software fail on you if you have an address in, say, the .info or .museum top-level domains because they only allow two-letter top-level domains + .com .net .org .gov .edu .mil?

Then RFC 3696 may be of interest to you. It may even be of interest if you hadn't had such problems but are interested in the larger picture of how to verify that URLs are correct or guessing at URLs from incomplete information.