comments on draft-ietf-idnabis-bidi

Tue Feb 10 18:22:33 CET 2009

Note that part of what Mati is suggesting is that simplified rules can meet
the objectives in the bidi document. For that, Harald (and Erik) would have
to run their tools to see if the suggested rules still work, and point Mati
to problem cases if they don't.

Mark

On Tue, Feb 10, 2009 at 06:36, Vint Cerf <vint at google.com> wrote:

> thanks for these precise comments, Mati.
> Harald, I hope you can assess and incorporate as appropriate into a revised
> draft.
>
> vint
>
>
> Vint Cerf
> Google
> 1818 Library Street, Suite 400
> Reston, VA 20190
> 202-370-5637
> vint at google.com
>
>
>
>
> On Feb 10, 2009, at 3:28 AM, Matitiahu Allouche wrote:
>
>
> My attention was recently drawn to the subject document (version 03) and I
> have a number of comments.  Some of them are very minor (typos, editorial)
> and reflect my pedantic mind, but I thought that I could as well help
> improve the form of the document.  Other comments touch more to the essence,
> and I will appreciate considering them seriously.
>
> 1) In section 2, first paragraph, "satisifes" should be "satisfies".
>
> 2) Section 2, rule 1 mentions the "Character Grouping requirement" for the
> first time in the document.  Either there should be a forward reference to
> section 3 where it will be explained, or (better, in my opinion), the
> content of the current section 3 should precede the content of the current
> section 2.
>
> 3) In the sentence "ET is excluded because the string L ET does not
> satisfy the Character Grouping requirement.", "L" seems to represent a
> label, but can easily be confused with the L Bidi property (all the more
> since it is adjacent to ET which surely represents a character with the ET
> Bidi property).
>
> 4) In the sentence "CS is excluded because the string L CS does not
> satisfy the Character Grouping requirement.", "L" seems to represent a
> label, but can easily be confused with the L Bidi property (all the more
> since it is adjacent to CS which surely represents a character with the CS
> Bidi property).
>
> 5) I see no reason why CS is excluded while ES is allowed.  Both can be the
> source of the same kind of  violation of the Character Grouping requirement.
>  ES characters are excluded from the first and last positions by rules 2 and
> 3.  With the same restrictions (exclusion from the first and last
> positions), ES and ET characters can be allowed and will not violate the
> Character Grouping requirement any more than ES characters.
>
> 6) In section 1.1, there appears the following statement: "This
> specification is not intended to place any requirements on domain names that
> do not contain right-to-left characters."
> Also the title of section 2 is "A replacement for the RFC 3454 BIDI rule"
> which implies that the text only deals with "Bidi" labels.
> If that means that the specification applies only to labels which contain
> at least one character with Bidi property R, AL or AN, and we combine that
> with rule 4 "If an R, AL or AN is present, no L may be present.", then an
> L character can never be part of a Bidi label, and the L should be removed
> from the list of allowed Bidi properties in rule 1.
>
> 7) In [UAX9], rule X9 says that BN characters must be removed from the
> displayed text.  Any such invisible character violates the Label Uniqueness
> requirement.  BN characters must not be allowed by rule 1.
>
> 8) From rules 1, 2, 4, 6 and 7, plus our comments 6 and 7 above, it results
> that the first character of a Bidi label can only be of type R or AL.  Such
> a statement can advantageously replace rules 2, 6 and 7.
>
> 9) Rule 5 includes no justification.  While a mixture of AN and EN
> characters in the same label seems odd and not required in real life
> situations, it is not clear what requirement would be violated by such a
> combination.
>
> 10) The rules allow AN or EN digits to appear in the last position of a
> label (in opposition to RFC 3454).  Let us consider the following examples
> (where lower case letters represent L characters and upper case letters
> represent R or AL characters):
>
>    a. network order = "ABC123.456xyz"  display order (LTR) =
> "123.456CBAxyz"  display order (RTL) = "123.456xyzCBA"
>
>    b. network order = "ABC.456-xyz"  display order (LTR) = "456.CBA-xyz"
>  display order (RTL) = "xyz-456.CBA"
>
>    c. network order = "ABC123.456.xyz"  display order (LTR) =
> "123.456CBA.xyz"  display order (RTL) = "xyz.123.456CBA"
>
>    d. network order = "ABC.456.xyz"  display order (LTR) = "456.CBA.xyz"
>  display order (RTL) = "xyz.456.CBA"
>
> Examples a, b and c show very ugly violations of the Character Grouping
> requirement.  Since the document does not place requirements on non-Bidi
> labels, any non-Bidi label starting with digits following a Bidi label will
> cause a Character Grouping violation.  If Bidi labels are restricted from
> ending with digits (optionally followed by NSMs), then non-Bidi labels which
> contain only digits (example d) following a Bidi label will not cause a
> Character Grouping violation.
> Whether this modest benefit justifies imposing such a restriction is
> subject to discussion.
>
> 11) Towards the end of section 2, there appears the following sentence: "In
> a domain name consisting of only labels that pass the test, the requirements
> of Section 3 are satisfied."
> This is not true for domain names like in the examples above, unless
> non-Bidi labels are excluded, which is a very hard constraint.
>
> 12) The next sentence says: "In a domain name consisting of only
> LDH-labels and labels that pass the test, the requirements of Section 3 are
> satisfied as long as a label that starts with an ASCII digit does not come
> after a right-to-left label that ends in a digit."
> This is not true.  See example b above.
>
> 13) In section 3, there appears the sentence: "the label "123-456" will
> have a different display order in an RTL context than in a LTR context."
> This is not true, IMHO.  If the last letter before the label is not an
> Arabic Letter, it will be displayed as "123-456" both in LTR and RTL
> context.  If it is an Arabic Letter, it will be displayed as "456-123".
>
> 14) In section 3, there appears the sentence: "The Label Uniqueness
> property should hold true between LTR paragraphs and RTL paragraphs.  This
> was shown to be unsound."
> In fact, in all cases where Character Grouping and Label Uniqueness are
> satisfied for each paragraph direction separately, there will be Label
> Uniqueness between LTR and RTL paragraphs.
>
> 15) In section 3, since an "unproblematic label" can be a label which
> satisfies the requirements, the clause "any label S1 and S2 that is either
> a label satisfying the requirements or an unproblematic label" can be
> shortened to "any label S1 and S2 that is an unproblematic label".
>
> 16) In the formal statement of the Label Uniqueness requirement, there is
> no provision (or exclusion) for the case where L and L' are identical.
>
> 17) In summary I suggest that the rules in section 2 should be reformulated
> as below.
>
>    1.  Only characters with the BIDI properties R, AL, AN, EN, ES,
>       CS, ET, ON and NSM are allowed in RTL labels.
>
>   2.  The first position must be a character with Bidi property R or AL.
>
>   3.  The last position must be a character with Bidi property R or AL,
>        followed by zero or more NSM.
>
>   3 variant.  The last position must be a character with Bidi property R,
>      AL, EN or AN, followed by zero or more NSM.
>
>   4 (debatable).  If an EN is present, no AN may be present, and vice
>       versa.
>
> It can be seen that this formulation is quite close to that in RFC 3454,
> while solving all the problems that the subject document aims to solve.
>
>
> Shalom (Regards),  Mati
>           Bidi Architect
>           Globalization Center Of Competency - Bidirectional Scripts
>           IBM Israel
>           Phone: +972 2 5888802    Fax: +972 2 5870333    Mobile: +972 52
> 2554160
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