On 2/4/15 11:44 PM, Pete Resnick wrote:
On 2/4/15 3:05 PM, Peter Saint-Andre - &yet wrote:
I am thinking that this new text would be best in the Interoperability
Considerations section. Does that seem right?
I think that's reasonable. Perhaps split it, and make "13.1 General
Considerations" and "13.2 ???". It's a bit separate, so I don't know
that it should just be added as a paragraph, but I don't have a good
subsection title. I'll leave it to the authors.
Here is what I have in my working copy. Please note that to improve
readability I broke up some of the sentences in the long paragraph we
all agreed to. Please review.
###
13. Interoperability Considerations
13.1. Encoding
Although strings that are consumed in PRECIS-based application
protocols are often encoded using UTF-8 [RFC3629], the exact encoding
is a matter for the application protocol that uses PRECIS, not for
the PRECIS framework.
13.2. Character Sets
It is known that some existing systems are unable to support the full
Unicode character set, or even any characters outside the ASCII
range. If two (or more) applications need to interoperate when
exchanging data (e.g., for the purpose of authenticating a username
or password), they will naturally need to have in common at least one
coded character set (as defined by [RFC6365]). Establishing such a
baseline is a matter for the application protocol that uses PRECIS,
not for the PRECIS framework.
13.3. Unicode Versions
Changes to the properties of Unicode code points can occur as the
Unicode Standard is modified from time to time. For example, three
code points underwent changes in their GeneralCategory between
Unicode 5.2 (current at the time IDNA2008 was originally published)
and Unicode 6.0, as described in [RFC6452]. Implementers might need
to be aware that the treatment of these characters differs depending
on which version of Unicode is available on the system that is using
IDNA2008 or PRECIS. Other such differences might arise between the
version of Unicode current at the time of this writing (7.0) and
future versions.
13.4. Potential Changes to Handling of Certain Unicode Code Points
As part of the review of Unicode 7.0 for IDNA, a question was raised
about a newly-added code point that led to a re-analysis of the
Normalization Rules used by IDNA and inherited by this document
(Section 5.2.4). Some of the general issues are described in
[IAB-Statement] and pursued in more detail in
[I-D.klensin-idna-5892upd-unicode70].
At the time of writing, these issues have yet to be settled.
However, implementers need to be aware that this specification is
likely to be updated in the future to address these issues. The
potential changes include:
o The range of characters in the LetterDigits category
(Section 4.2.1 and Section 9.1) might be narrowed.
o Some characters with special properties that are now allowed might
be excluded.
o More "Additional Mapping Rules" (Section 5.2.2) might be defined.
o Alternative normalization methods might be added.
Nevertheless, implementations and deployments that are sensitive to
the advice given in this specification are unlikely to run into
significant problems as a consequence of these issues or potential
changes - specifically the advice to use the more restrictive
IdentifierClass whenever possible, or if using the FreeformClass to
allow only a restricted set of characters, particularly avoiding
characters whose implications they do not actually understand.
###
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