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Re: bidi properties from uniprop tables

From: Eli Zaretskii
Subject: Re: bidi properties from uniprop tables
Date: Fri, 19 Aug 2011 13:36:22 +0300

> From: "Stephen J. Turnbull" <address@hidden>
> Cc: address@hidden,
>     address@hidden
> Date: Fri, 19 Aug 2011 18:15:58 +0900
>     Unassigned characters are given strong types in the
>     algorithm. This is an explicit exception to the general Unicode
>     conformance requirements with respect to unassigned characters. As
>     characters become assigned in the future, these bidirectional
>     types may change. For assignments to character types, see
>     DerivedBidiClass.txt [DerivedBIDI] in the [UCD].

Thanks, I've managed to miss that addition to the UBA.

> Since Bidi_Class is only used in this algorithm (and explicit property
> lookups) AFAIK

That's not true, it is also used in regexp search by category.  So we
should decide whether to assign these types in the uniprop table, or
have a fallback for them in bidi.c.  Any opinions?  Handa-san?

> it seems reasonable to me that get-char-code-property
> et amis should return the "strong type" specified by DerivedBIDI
> (which is LTR it seems, but you should check that).

No, the type depends on the block:

  # Unlike other properties, unassigned code points in blocks
  # reserved for right-to-left scripts are given either types R or AL.
  # The unassigned code points that default to AL are in the ranges:
  #     [\u0600-\u07BF \uFB50-\uFDFF \uFE70-\uFEFF]
  #     Arabic:            U+0600  -  U+06FF
  #     Syriac:            U+0700  -  U+074F
  #     Arabic_Supplement: U+0750  -  U+077F
  #     Thaana:            U+0780  -  U+07BF
  #     Arabic_Presentation_Forms_A:
  #                        U+FB50  -  U+FDFF
  #     Arabic_Presentation_Forms_B:
  #                        U+FE70  -  U+FEFF
  #           minus noncharacter code points.
  # The unassigned code points that default to R are in the ranges:
  #     [\u0590-\u05FF \u07C0-\u08FF \uFB1D-\uFB4F \U00010800-\U00010FFF 
  #     Hebrew:            U+0590  -  U+05FF
  #     NKo:               U+07C0  -  U+07FF
  #     Cypriot_Syllabary: U+10800 - U+1083F
  #     Phoenician:        U+10900 - U+1091F
  #     Lydian:            U+10920 - U+1093F
  #     Kharoshthi:        U+10A00 - U+10A5F
  #     and any others in the ranges:
  #                        U+0800  -  U+08FF,
  #                        U+FB1D  -  U+FB4F,
  #                        U+10840 - U+10FFF,
  #                        U+1E800 - U+1EFFF
  # For all other cases:

  #  All code points not explicitly listed for Bidi_Class
  #  have the value Left_To_Right (L).

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