UAX 29 questions
Mark Davis ☕️
mark at macchiato.com
Fri Jan 30 02:32:56 CST 2015
I apology in advance that I'm running low on time, and didn't go through
all the messages on this thread carefully. So I may not be fully
appreciating people's positions. I'm just making some quick points about 2
items that caught my eye.
1. There are certainly times where two rules in sequence may overlap, just
X Y* x Z
Y x Z* W
The first rule could trigger on X Y Z W, even though the second would also
trigger on it. This may or may not be "sloppiness"; sometimes it simply
makes the second rule too convoluted to also exclude triggering on
everything that could possibly trigger earlier.
That being said, if there simplifications in the rules that would make it
clearer, I'd suggest submitting a proposal for that. The UTC is meeting
next week, and could consider it either then or at subsequent meetings.
Note: the HTML files in http://unicode.org/Public/UNIDATA/auxiliary/ have a
number of sample cases (which are also used in the test files). Hovering
over boundaries in those sample cases shows which rule is triggered, such
We're always open to additional samples that are illustrative of how the
rules work. As I thought about your message, it became clear to me that it
would be useful to have a complete enough set of sample cases that each
rule is triggered by at least one case, if you or anyone else is interested
in helping to add those.
2. Also, the following 2 rules are not equivalent:
a) Any × (Format | Extend)
b) X (Extend | Format)* → X
(b) implies (a), but not the reverse. The difference is on the right side
of characters. Rule b, affects every subsequent rule, and can be viewed as
a shorthand. After it, we can just say:
A B × C D
And that has the effect of saying:
A (Extend | Format)* B (Extend | Format)* × C (Extend | Format)* D
See also http://unicode.org/reports/tr29/#Grapheme_Cluster_and_Format_Rules
However, it may not be clear that (b) implies (a); that might be what you
are getting at. If so, then we could add an explicit statement to that
*— Il meglio è l’inimico del bene —*
On Thu, Jan 29, 2015 at 7:52 PM, Karl Williamson <public at khwilliamson.com>
> On 01/25/2015 05:14 AM, Philippe Verdy wrote:
>> This is not a contradiction.
> At the very least it is too sloppy for a standard. Once there is a match
> in the list of rules, later rules shouldn't have to be looked at. I'll
> submit a formal feedback form.
> But there is another issue as well. I do not see how the specified rules
> when applied to the sequence of code points:
> U+0041 U+200D U+0020
> cause the ZWJ, an Extend, to not break with the "A", an ALetter.
> Rule WB4 is
> "Ignore Format and Extend characters, except when they appear at the
> beginning of a region of text.".
> Not clearly stated, but it appears to me that the ZWJ must be considered
> here to be the beginning of a region of text, as we are looking at the
> boundary between it and the "A". No rule specifically mentions ALetter
> followed by an Extend, so by the default rule, WB14
> "Otherwise, break everywhere (including around ideographs)"
> this should be a word break position. But that is absurd, as the Extend
> is supposed to extend what precedes it. If I add a rule
> "Don't break before Extend or Format"
> × (Extend | Format)
> my implementation passes all tests. I added this rule before WB4.
>> combine the two rules and they are equivalent to these two alternate
>> WB56 can be read as these two:
>> (WB56a) ALetter × (MidLetter | MidNumLet | Single_Quote) (ALetter |
>> (WB56b) Hebrew_Letter × (MidLetter | MidNumLet | Single_Quote)
>> (ALetter | Hebrew_Letter)
>> Then add :
>> (WB57) Hebrew_Letter × Single_Quote
>> it just removes the condition of a letter following the quote in WB56b.
>> So that WB56b and WB57 can be read as equivalent to these two:
>> (WB56c) Hebrew_Letter × (MidLetter | MidNumLet) (ALetter |
>> (WB57) Hebrew_Letter × Single_Quote
>> But you cannot merge any of these two last rules in a single rule for
>> 2015-01-25 7:26 GMT+01:00 Karl Williamson <public at khwilliamson.com
>> <mailto:public at khwilliamson.com>>:
>> I vaguely recall asking something like this before, but if so, I
>> didn't save the answers, and a search of the archives didn't turn up
>> Some of the rules in UAX #29 don't make sense to me.
>> For example, rule WB7a
>> Hebrew_Letter × Single_Quote
>> seems to say that a Hebrew_Letter followed by a Single Quote
>> shouldn't break. (And Rule WB4 says that actually there can be
>> Extend and Format characters between the two and those should be
>> But the earlier rule, WB6
>> (ALetter | Hebrew_Letter) × (MidLetter | MidNumLet |
>> Single_Quote) (ALetter | Hebrew_Letter)
>> seems to me to say (among other things) that a Hebrew Letter
>> followed by a Single Quote shouldn't break if and only if the latter
>> is also followed by either an ALetter or another Hebrew Letter
>> (again modulo ignored Format and Extend letters)
>> This seems contradictory. One rule says something unconditionally,
>> and the other rule adds conditions.
>> Unicode mailing list
>> Unicode at unicode.org <mailto:Unicode at unicode.org>
> Unicode mailing list
> Unicode at unicode.org
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