Re: Jumping Cursor. Was: Right-to-Left Punctuation Problem

From: Mark Davis (mark.davis@icu-project.org)
Date: Tue Aug 02 2005 - 20:34:33 CDT

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    The choice of whether or not to clone characters was made consciously. We
    had experience with the other model: I wrote the first implementation of
    Arabic and Hebrew on the Mac back in 1986ish, and in that implementation
    cloned the common characters, giving the clones RTL directionality.

    We found many problems with this, because identical-looking characters had
    bizarre effects when cut and pasted into different fields. Arabic and Hebrew
    users are not working in a vacuum; they will be cutting and pasting in text
    from a variety of sources, including LTR sources. Cloning parentheses (or
    interpreting them according to visual appearance) meant that every program
    that analyzed text for open/close parentheses (eg regex) failed. And we
    didn't do numbers as LSDF (least-significant digit first); that would have
    caused huge problems in compatibility because software is just not set up to
    recognize LSDF numbers. And this is not to speak of the security problems
    with these clones (see http://www.unicode.org/reports/tr36/).

    Thus when it came time to do the original BIDI algorithm, we decided not to
    use the cloning approach.

    The BIDI algorithm is not an impediment to the development of software
    globalized for BIDI. Most programs will simply use OS-supported text widgets
    that handle all the details for them. Text/Word processors can use the
    lower-level implementations of the BIDI algorithm: there are plenty of solid
    implementations around, either supported by the OS or in libraries like ICU.
    The barriers that I have seen to people globalizing their products for BIDI
    are more the other aspects, such as dialog layout in the applications, etc.

    Moreover, it would be certainly possible for a program to use visual layout
    on the screen, then translate that internal format to and from logical
    layout for transmission as Unicode. Quite frankly, while you find the BIDI
    algorithm difficult to use, all of the other approaches had such serious
    problems that it is really the only practical approach.

    (Notwithstanding that, if I had the chance to go back in time and undo a few
    things, I would have simplified the weak processing to make numbers
    independent of their surroundings. But that's water far, far under the
    bridge.)

    ‚ÄéMark

    ----- Original Message -----
    From: "Gregg Reynolds" <unicode@arabink.com>
    To: "John Hudson" <tiro@tiro.com>
    Cc: "'Unicode'" <unicode@unicode.org>
    Sent: Tuesday, August 02, 2005 17:33
    Subject: Re: Jumping Cursor. Was: Right-to-Left Punctuation Problem

    > John Hudson wrote:
    > > Gregg Reynolds wrote:
    > >
    > >> Adding to the already existing - what, 5? 6? - different ways of
    > >> encoding each digit. Let's count the ways:
    > >>
    > >> 0030-0039 DIGIT ZERO etc
    > >> 0660-0069 ARABIC-INDIC
    > >> 06F0-06F9 EXTENDED ARABIC-INDIC
    > >> 0966-096F DEVANAGARI
    > >> 09E6-09EF BENGALI
    > >> 0A66-0A6F GURMUKHI
    > >> 0AE6-0AEF GUJARATI
    > >> Oriya, Tamil, Telugu, Kannada, Malayalam, Thai, Lao, Tibetan,
    > >> Myanmar, Ethiopic, Khmer, Mongolian, Limbu, Osmanya, various
    > >> mathematical digit characters, Japanese full-width, etc. etc. Twenty
    > >> one and counting.
    > >
    > >
    > > Most of which look different, some of which function differently (i.e.
    > > use different counting systems that do not correspond to our decimal
    > > digit system). I don't think there is any expectation that one would be
    > > able to perform cross-script arithmetic using Mongolian and Ethiopic
    > > numeral characters. What you are proposing is something quite other: two
    > > ways of encoding the *same* numerals. Your new numerals would look the
    > > same, represent the same numbers, need to be considered the same for
    > > searches, sorts and mathematical functions. They would be, in fact, the
    > > same characters encoded twice.
    > >
    >
    > Ok. I agree that is a valid observation. I think, anyway. I have to
    > ponder it a bit more. I think it depends on what the meaning of "same"
    > is. Aren't 0030-9 and 0660-9 really the "same"? My understanding of
    > unicode is that it doesn't address these semantics - 0-9 are just
    > characters, not mathematical signs. (The fact that the have "number"
    > property only means they all have the same formal category, not that
    > they denote mathematical values; it could just as easily have been
    > called the "fdsaflkh" property. It's up to a higher level protocol to
    > interpret "fdsaflkh" characters as mathematical signs.) Mathematically,
    > any characters that denote the mathematical values 0-9 may be considered
    > "the same", regardless of graphical form. The latter is a mere matter
    > of implementation (font) technology.
    >
    > > But this is the kicker, as already mentioned yesterday: *all* those
    > > numerals characters you listed share the same directionality, and all
    > > numbers in Unicode are encoded most-significant digit first. Maybe if
    >
    > Well, typographically they are all LTR, but that is completely
    > orthogonal to encoding syntax (polarity). It occurs to me now that
    > you've put your finger on the problem. Which is, that these
    > "characters" should in fact be treated as characters, and not
    > mathematical signs, in order to be consistent (ha!) with Unicode
    > principles. Mathematical interpretation comes in at a higher
    > level protocol. This is consistent with Unicode design principles, as I
    > understand them. So assume that RTL 0-9 are just another set of
    > characters, w/out mathematical semantics, that all happen to have a
    > property called "number". They will be treated no differently than any
    > other RTL character w/r/t typesetting; w/r/t to math routines, they will
    > be treated no differently than any other "number" characters (math
    > routines must merely interpret polarity correctly.) In fact, there is
    > no need to stipulate any graphical form. (I note that MSWord happily
    > changes the form of numeric digit characters from European to Arabic
    > Indic based on user preferences. Does it change the underlying
    > encoding? Dunno, never checked.)
    >
    > > computing had been invented in the Middle East it would be the other way
    > > around, with the least significant digit encoded first, and the various
    > > standards would oblige all LTR writing systems to function
    > > bidirectionally with regard to numerals.
    >
    > But the point is that absolute directional is not the only design
    > choice. We would get along just fine with relative polarity (relative
    > to writing direction, that is.)
    >
    > >
    > > Now, when it comes to things like parentheses, the mirrored stuff does
    > > my head in and I really don't see the point of it. I'm guessing that it
    > > confuses application developers also, since it is implemented with so
    > > little consistency.
    >
    > You can say that again. But in this respect Unicode is already
    > obsolete. The only justification I can see for ambiguous
    > directionality, mirroring, etc. is trying to save space (code space, I
    > mean). Fifty years from now (or ten?) chars will be 64 bits, with an
    > essentially infinite code space, so there will be no justification for
    > either unification or directional ambiguity.
    >
    > -gregg
    >
    >
    >



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