HYPHEN-MINUS

[Wil Tan]

Chris,

2009/7/29 Patrik Fältström <patrik at frobbit.se>

> On 28 jul 2009, at 16.50, Chris Wright wrote:
>
> CONTEXTO for HYPHEN-MINUS
>>
>> * Is similar to the section in the protocol disallowing consecutive
>> hyphens in the third and fourth position (4.2.3.1 of protocol document)
>
>
 Agreed. It should be specified in the same place.


>> * Is applied to Unicode labels; the encoded label does not violate host
>> name syntax
>
>
Agreed.


>
>> * Has no context; the surrounding characters do not influence this test
>
>
While not dependent on surrounding characters, this test does hinge on the
position of the character in the label.


>
>>
>> I assume the rationale behind the prohibition of HYPHEN-MINUS at the
>> beginning or end of a label is to carry across host name syntax restrictions
>> into the Unicode label space. This appears to be attempting to achieve
>> similar goals to section 4.2.3.1 in the protocol document by disallowing
>> consecutive hyphens in the third and fourth positions. These two
>> restrictions should appear in the same place.
>>
>> To clear any confusion that may have arisen during limited discussion last
>> week, the context rule is applied to the putative U-label, therefore the DNS
>> and host name syntax restrictions do not apply (yet). Consider the label
>> b[U+00FC]cher-. The output of this label through the punycode algorithm when
>> appended with the ACE prefix gives gives xn--bcher--3ya. Note this label
>> conforms to the host name syntax.
>>
>> Thus for consistency, simplicity and clarity sake I propose the following:
>>
>> In protocol change:
>>
>> 4.2.3.1. Consecutive Hyphens
>> The Unicode string MUST NOT contain "--" (two consecutive hyphens) in the
>> third and fourth character positions.
>>
>> to
>>
>> 4.2.3.1. Hyphen Restrictions
>> The Unicode string MUST NOT contain "--" (two consecutive hyphens) in the
>> third and fourth character positions and MUST NOT start or end with a "-"
>> (hyphen).
>>
>> And then remove the context rule from the tables document and return
>> hyphen to PVALID status as with all other LDH characters
>>
>
Alternatively, have the two consecutive hyphens rule in the CONTEXTO as
well.
There are pros and cons about having the rules in the protocol versus as a
contextual rule. In any case, having it in the same place makes sense.

=wil
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