[idn] Mixed TC/SC (was Re: Layer 2 and "idn identities")

[David Hopwood <david.hopwood@zetnet.co.uk>]

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liana Ye wrote:
> We are discussing how the registrars to "avoid registering mixed scripts
> 'names' ". Can you suggest any way of doing this, or any feasible guidelines?

It's fairly trivial: define a formal syntax that registrars can check
against for domains that should exclude mixed names.

The general form of that syntax would be:

['\' means set difference, '/' means union, '&' means intersection]

  SCONLY = ... ; set of Han ideograph code points that are only used in SC
  TCONLY = ... ; set of Han ideograph code points that are only used in TC

  ; a string that is not mixed either contains no SCONLY code points,
  ; or no TCONLY codepoints.
  NotMixed = *(UNICODE \ SCONLY) / *(UNICODE \ TCONLY)

  HostString = ... ; whatever syntax is decided on
  NotMixedHostString = NotMixed & HostString


If you want to allow mixed TC/SC in strings that also contain Katakana,
Hiragana, Bopomofo or Hangul (on the grounds that these are not Chinese),
then define:

  MixedAllowed = *UNICODE (Scripts:HIRAGANA /
                           Scripts:KATAKANA /
                           Scripts:BOPOMOFO /
                           Scripts:HANGUL) *UNICODE

  AllowedHostString = (NotMixed / MixedAllowed) & HostString


Note that SCONLY and TCONLY can include code points that would have
1-many and many-1 mappings for TC/SC conversion, as well as 1-1 mappings.

- -- 
David Hopwood <david.hopwood@zetnet.co.uk>

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