Archaic scripts

Mark Davis mark.davis at
Fri May 9 03:30:13 CEST 2008

I agree.

On Thu, May 8, 2008 at 4:01 PM, Erik van der Poel <erikv at> wrote:

> An unassigned codepoint may be assigned to an uppercase letter. So a
> piece of software that looks up purported U-labels must check whether
> it contains any unassigned codepoints. So we should recommend that
> such software be restricted (follow certain rules), in order to
> achieve interoperability. (MSIE7 refuses to look up domain names
> containing unassigned characters.)
> If we lock down the DISALLOWED set too tightly, we may regret it
> later. One way to avoid locking it down is to recommend that
> burned-in-ROM and other unupgradable software only use protocols that
> use LDH- and A-labels. All pieces of software, whether IDNA-aware or
> not, are explicitly permitted to look up Punycode labels, without
> decoding them to check for DISALLOWED, CONTEXT*, etc.
> On the other hand, we should recommend that protocol and application
> developers only use U-labels if they are willing to make their
> software upgradable. They need to do this for unassigned codepoints
> anyway. So we might as well allow for the possibility of moving some
> characters from DISALLOWED to other categories (if and when we
> determine that they should be moved, having come up with better
> criteria for use in IDNs, more information, clamoring users, etc).
> If we allow for this possibility, we don't need to fret so much about
> historic scripts right now. Just dump them in DISALLOWED for now, and
> deal with them later, if they ever need to be dealt with.
> Erik
> On Thu, May 8, 2008 at 1:59 PM, Shawn Steele <Shawn.Steele at>
> wrote:
> > Erik wrote:
> >
> >  > This also neatly solves the problem of whether or not IDNA-unaware and
> >  > IDNA-aware clients are allowed to look up labels with Punycode in
> >  > them. They should always be allowed to do so. Only software that tries
> >  > to convert from U-labels to A-labels needs to be restricted. This is
> >  > how we can achieve the most reasonable level of interoperability, in
> >  > my opinion.
> >
> >  I think that conversion U to A conversion does NOT need restriction.
>  Assuming that the steps in conversion include NFKC or appropriate mappings,
> then if a character moves from disallowed to allowed, the conversion is
> already known.  So no change is required for lookup, even if conversion is
> required. The only change would be the software the decides the legality of
> the name, which, IMO could be at a different layer.
> >
> >  - Shawn
> >
> >
> >
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> >
> >
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