Reviewer's summary:

The document touches right on typical ART issues such as the hard parts
of internationalization and evolution -- but works in a space where
there is little room for change, and applies technical enhancements
where it can.

Apart from technical fixes, it has relatively stern words for registries
that ignored the already existing guidance that is emphasized and
precised in this document; whether that can lead to a change in behavior
is beyond what I can confidently make predictions about.


I consider the document ready; the issues below are minor enough that
they should easily be addressable by the authors and the RFC editor
without further review.


Unclear errata handling:

* Erratum 5484 is bundled with the group of 63-character-A-label vs.
  252-octet-U-label, when <https://www.rfc-editor.org/errata/eid5484>
  looks completely unrelated.

Editorial remarks:

* Section 4, the paragraph "Rules requiring strict" gave the right gist at
  quick skimming, but took several attempts for me to fully parse in
  detail. It might be easier to consume with simplified sentence
  structure.

* "When RFC 5891 is actually updated": This document does update 5891 if
  approved, and the Unicode references are relatively recent -- is this a
  leftover comment from during editing, or more of a remark to the RFC
  editor?

Editorial nits:

* "Section 2.3.2.3 of the Definitions document" would be more usable as a
  deep link into the RFC, samey with any later occurrence of "Section"
  that is not a link.

* "IDNA2008" and "IDNA 2008" is inconsistently used with and without
  the space character.

* 5.2 New, has more closing than open parantheses, the closing parenthesis
  after UnicodeB should be removed.