Re: Public Review Issue 232 Proposed Update UAX #9, Unicode Bidirectional Algorithm (Copy of email sent to the list; also posted by me to unicode feedback/public review issue-- but this has not yet posted there)

From: CE Whitehead <>
Date: Tue, 29 Jan 2013 19:00:24 -0500


From: Philippe Verdy <>

Date: Fri, 25 Jan 2013 05:21:39 +0100

> Letter-like mathematical symbols are those like Product (Greek capital

> Pi), Sum (Greek capital Sigma). Mirroring them by default would have

> strange effects, even if they may be mirrored in formulas.

> Lower-than and Higher-than symbols are not letter-like and are safe to

> mirror, they behave like parentheses.

> . . .
> Our problem for now is the "best-fit" pairing (rule HL6 really hurts

> and offers absolutely no benefit, it causes havoc an interoperability

> problems ; it should be admitted ONLY for PUA characters, or for

> out-of-band markup syntax in a rich-text format because they are

> supposed to be rendered as isolates in code editors). For the

> stability of BiDi, this should not happen. Mirrorable pairs should be

> definitely stabilized
Perhaps some quotation-type marks may be mirrorable according to language-specific principles, for example French guillemets
 English I learned the following " ' ' "; the semi-colon might also go
inside in some instances IMO though normally not; I'm not using any but
ascii symbols here).

I don't think dashes should be mirrored at
all however. (Many of my dashes -- for example these -- are quite
symmetrical; but others are not -- I sometimes have a closing dash and
sometimes not; but Emily Dickinson is really the expert on the use of
the dash: There's no real reason for mirroring these.)

 can I personally think of any reason to mirror mathematical symbols such as pi,
square root, or sigma; maybe there would be mirroring for absolute value
 symbols, as well as symbols for matrices, floors, ceilings? (like for parentheses; for examples see I guess -- I'm not a mathematician); so perhaps these specific symbols can be included in the algorithm. (If anyone can give examples of others they can be included too; but Phillipe has said this should be stabilized, and probably it should be.)

 recall that Phillipe suggested previously that there might be
language-specific and locale-specific tailoring for quotation marks
according to CLDR but even within languages there are multiple options
apparently sometimes and this could cause confusion. Here's Phillipe's
post on this:

 I think it was agreed that the bidi parenthese algorithm would thus
focus on brackets and parentheses though maybe for some languages such
as English or French language-specific tailoring would work o.k. for
quotation marks.

Back to brackets and parentheses: I personally do not think that it is
 important whether the brackets mirrored follow conventions like ([]) or
 not; I think it's fine to mirror also (()) or {{}} -- and isnot some of
 this is going to be specific to the domain (programming versus other

(Sorry for this late late post on this topic, a topic which I suppose has just about been "driven into the ground.")


--C. E. Whitehead
Received on Tue Jan 29 2013 - 18:07:19 CST

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