It might be useful to add some best practices related to IDNs, maybe to the Resource identifiers section, or a new section.

For example, in w3c/rdf-concepts#63 there are some guidelines like:

Contemporary documents should not be referring to Punycode at all, especially as a type of string, but should be using the IDNA2008 terminology of "A-labels" and "U-labels", defined in RFC 5890.