draft-ietf-precis-framework-09.txt   draft-ietf-precis-framework-10.txt 
PRECIS P. Saint-Andre PRECIS P. Saint-Andre
Internet-Draft Cisco Systems, Inc. Internet-Draft Cisco Systems, Inc.
Obsoletes: 3454 (if approved) M. Blanchet Obsoletes: 3454 (if approved) M. Blanchet
Intended status: Standards Track Viagenie Intended status: Standards Track Viagenie
Expires: January 11, 2014 July 10, 2013 Expires: April 18, 2014 October 15, 2013
PRECIS Framework: Preparation and Comparison of Internationalized PRECIS Framework: Preparation and Comparison of Internationalized
Strings in Application Protocols Strings in Application Protocols
draft-ietf-precis-framework-09 draft-ietf-precis-framework-10
Abstract Abstract
Application protocols using Unicode code points in protocol strings Application protocols using Unicode code points in protocol strings
need to properly prepare such strings in order to perform valid need to properly prepare such strings in order to perform valid
comparison operations (e.g., for purposes of authentication or comparison operations (e.g., for purposes of authentication or
authorization). This document defines a framework enabling authorization). This document defines a framework enabling
application protocols to perform the preparation and comparison of application protocols to perform the preparation and comparison of
internationalized strings (a.k.a. "PRECIS") in a way that depends on internationalized strings (a.k.a. "PRECIS") in a way that depends on
the properties of Unicode code points and thus is agile with respect the properties of Unicode code points and thus is agile with respect
to versions of Unicode. As a result, this framework provides a more to versions of Unicode. As a result, this framework provides a more
sustainable approach to the handling of internationalized strings sustainable approach to the handling of internationalized strings
than the previous framework, known as Stringprep (RFC 3454). A than the previous framework, known as Stringprep (RFC 3454). This
specification that reuses this framework can either directly use the document obsoletes RFC 3454.
PRECIS string classes or subclass the PRECIS string classes as
needed. This framework takes an approach similar to the revised
internationalized domain names (IDNs) in applications (IDNA)
technology (RFC 5890, RFC 5891, RFC 5892, RFC 5893, RFC 5894) and
thus adheres to the high-level design goals described in the IAB's
recommendations regarding IDNs (RFC 4690), albeit for application
technologies other than the Domain Name System (DNS). This document
obsoletes RFC 3454.
Status of this Memo Status of this Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 11, 2014.
This Internet-Draft will expire on April 18, 2014.
Copyright Notice Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the Copyright (c) 2013 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. String Classes . . . . . . . . . . . . . . . . . . . . . . . . 6 3. String Classes . . . . . . . . . . . . . . . . . . . . . . . . 6
3.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . 6 3.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . 6
3.2. Order of Operations . . . . . . . . . . . . . . . . . . . 8 3.2. IdentifierClass . . . . . . . . . . . . . . . . . . . . . 7
3.3. IdentifierClass . . . . . . . . . . . . . . . . . . . . . 8 3.3. FreeformClass . . . . . . . . . . . . . . . . . . . . . . 8
3.4. FreeformClass . . . . . . . . . . . . . . . . . . . . . . 10 4. Profiles . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
4. Use of PRECIS String Classes . . . . . . . . . . . . . . . . . 12 4.1. Principles . . . . . . . . . . . . . . . . . . . . . . . . 10
4.1. Principles . . . . . . . . . . . . . . . . . . . . . . . . 12 4.2. Building Application-Layer Constructs . . . . . . . . . . 12
4.2. Subclassing . . . . . . . . . . . . . . . . . . . . . . . 13 4.3. A Note about Spaces . . . . . . . . . . . . . . . . . . . 12
4.3. Building Application-Layer Constructs . . . . . . . . . . 14 5. Order of Operations . . . . . . . . . . . . . . . . . . . . . 13
4.4. A Note about Spaces . . . . . . . . . . . . . . . . . . . 14 6. Code Point Properties . . . . . . . . . . . . . . . . . . . . 13
5. Code Point Properties . . . . . . . . . . . . . . . . . . . . 15 7. Category Definitions Used to Calculate Derived Property . . . 15
6. Category Definitions Used to Calculate Derived Property 7.1. LetterDigits (A) . . . . . . . . . . . . . . . . . . . . . 16
Value . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 7.2. Unstable (B) . . . . . . . . . . . . . . . . . . . . . . . 16
6.1. LetterDigits (A) . . . . . . . . . . . . . . . . . . . . . 17 7.3. IgnorableProperties (C) . . . . . . . . . . . . . . . . . 16
6.2. Unstable (B) . . . . . . . . . . . . . . . . . . . . . . . 17 7.4. IgnorableBlocks (D) . . . . . . . . . . . . . . . . . . . 16
6.3. IgnorableProperties (C) . . . . . . . . . . . . . . . . . 17 7.5. LDH (E) . . . . . . . . . . . . . . . . . . . . . . . . . 17
6.4. IgnorableBlocks (D) . . . . . . . . . . . . . . . . . . . 17 7.6. Exceptions (F) . . . . . . . . . . . . . . . . . . . . . . 17
6.5. LDH (E) . . . . . . . . . . . . . . . . . . . . . . . . . 18 7.7. BackwardCompatible (G) . . . . . . . . . . . . . . . . . . 18
6.6. Exceptions (F) . . . . . . . . . . . . . . . . . . . . . . 18 7.8. JoinControl (H) . . . . . . . . . . . . . . . . . . . . . 19
6.7. BackwardCompatible (G) . . . . . . . . . . . . . . . . . . 19 7.9. OldHangulJamo (I) . . . . . . . . . . . . . . . . . . . . 19
6.8. JoinControl (H) . . . . . . . . . . . . . . . . . . . . . 20 7.10. Unassigned (J) . . . . . . . . . . . . . . . . . . . . . . 19
6.9. OldHangulJamo (I) . . . . . . . . . . . . . . . . . . . . 20 7.11. ASCII7 (K) . . . . . . . . . . . . . . . . . . . . . . . . 19
6.10. Unassigned (J) . . . . . . . . . . . . . . . . . . . . . . 20 7.12. Controls (L) . . . . . . . . . . . . . . . . . . . . . . . 20
6.11. ASCII7 (K) . . . . . . . . . . . . . . . . . . . . . . . . 20 7.13. PrecisIgnorableProperties (M) . . . . . . . . . . . . . . 20
6.12. Controls (L) . . . . . . . . . . . . . . . . . . . . . . . 21 7.14. Spaces (N) . . . . . . . . . . . . . . . . . . . . . . . . 20
6.13. PrecisIgnorableProperties (M) . . . . . . . . . . . . . . 21 7.15. Symbols (O) . . . . . . . . . . . . . . . . . . . . . . . 20
6.14. Spaces (N) . . . . . . . . . . . . . . . . . . . . . . . . 21 7.16. Punctuation (P) . . . . . . . . . . . . . . . . . . . . . 20
6.15. Symbols (O) . . . . . . . . . . . . . . . . . . . . . . . 21 7.17. HasCompat (Q) . . . . . . . . . . . . . . . . . . . . . . 21
6.16. Punctuation (P) . . . . . . . . . . . . . . . . . . . . . 21 7.18. OtherLetterDigits (R) . . . . . . . . . . . . . . . . . . 21
6.17. HasCompat (Q) . . . . . . . . . . . . . . . . . . . . . . 22 8. Calculation of the Derived Property . . . . . . . . . . . . . 21
6.18. OtherLetterDigits (R) . . . . . . . . . . . . . . . . . . 22 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 22
7. Calculation of the Derived Property . . . . . . . . . . . . . 22 9.1. PRECIS Derived Property Value Registry . . . . . . . . . . 22
8. Code Points . . . . . . . . . . . . . . . . . . . . . . . . . 23 9.2. PRECIS Base Classes Registry . . . . . . . . . . . . . . . 22
9. Security Considerations . . . . . . . . . . . . . . . . . . . 23 9.3. PRECIS Profiles Registry . . . . . . . . . . . . . . . . . 23
9.1. General Issues . . . . . . . . . . . . . . . . . . . . . . 23
9.2. Use of the IdentifierClass . . . . . . . . . . . . . . . . 24 10. Security Considerations . . . . . . . . . . . . . . . . . . . 25
9.3. Use of the FreeformClass . . . . . . . . . . . . . . . . . 24 10.1. General Issues . . . . . . . . . . . . . . . . . . . . . . 25
9.4. Local Character Set Issues . . . . . . . . . . . . . . . . 24 10.2. Use of the IdentifierClass . . . . . . . . . . . . . . . . 25
9.5. Visually Similar Characters . . . . . . . . . . . . . . . 25 10.3. Use of the FreeformClass . . . . . . . . . . . . . . . . . 25
9.6. Security of Passwords . . . . . . . . . . . . . . . . . . 26 10.4. Local Character Set Issues . . . . . . . . . . . . . . . . 26
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 27 10.5. Visually Similar Characters . . . . . . . . . . . . . . . 26
10.1. PRECIS Derived Property Value Registry . . . . . . . . . . 27 10.6. Security of Passwords . . . . . . . . . . . . . . . . . . 28
10.2. PRECIS Base Classes Registry . . . . . . . . . . . . . . . 27 11. Interoperability Considerations . . . . . . . . . . . . . . . 28
10.3. PRECIS Subclasses Registry . . . . . . . . . . . . . . . . 29 12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 29
10.4. PRECIS Usage Registry . . . . . . . . . . . . . . . . . . 29 12.1. Normative References . . . . . . . . . . . . . . . . . . . 29
11. Interoperability Considerations . . . . . . . . . . . . . . . 31 12.2. Informative References . . . . . . . . . . . . . . . . . . 29
12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 31 Appendix A. Codepoint Table . . . . . . . . . . . . . . . . . . . 32
12.1. Normative References . . . . . . . . . . . . . . . . . . . 31 Appendix B. Acknowledgements . . . . . . . . . . . . . . . . . . 62
12.2. Informative References . . . . . . . . . . . . . . . . . . 32 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 62
Appendix A. Codepoint Table . . . . . . . . . . . . . . . . . . . 34
Appendix B. Acknowledgements . . . . . . . . . . . . . . . . . . 64
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 65
1. Introduction 1. Introduction
As described in the problem statement for the preparation and As described in the problem statement for the preparation and
comparison of internationalized strings ("PRECIS") [RFC6885], many comparison of internationalized strings ("PRECIS") [RFC6885], many
IETF protocols have used the Stringprep framework [RFC3454] as the IETF protocols have used the Stringprep framework [RFC3454] as the
basis for preparing and comparing protocol strings that contain basis for preparing and comparing protocol strings that contain
Unicode code points [UNICODE] outside the ASCII range [RFC20]. The Unicode code points [UNICODE] outside the ASCII range [RFC20]. The
Stringprep framework was developed during work on the original Stringprep framework was developed during work on the original
technology for internationalized domain names (IDNs), here called technology for internationalized domain names (IDNs), here called
skipping to change at page 5, line 36 skipping to change at page 4, line 36
([RFC5890], [RFC5891], [RFC5892], [RFC5893], [RFC5894]), no longer ([RFC5890], [RFC5891], [RFC5892], [RFC5893], [RFC5894]), no longer
use Stringprep and Nameprep. This migration away from Stringprep for use Stringprep and Nameprep. This migration away from Stringprep for
IDNs has prompted other "customers" of Stringprep to consider new IDNs has prompted other "customers" of Stringprep to consider new
approaches to the preparation and comparison of internationalized approaches to the preparation and comparison of internationalized
strings (a.k.a. "PRECIS"), as described in [RFC6885]. strings (a.k.a. "PRECIS"), as described in [RFC6885].
This document defines a framework for a post-Stringprep approach to This document defines a framework for a post-Stringprep approach to
the preparation and comparison of internationalized strings in the preparation and comparison of internationalized strings in
application protocols, based on several principles: application protocols, based on several principles:
1. Define a small set of string classes appropriate for common 1. Define a small set of string classes that specify the code points
application protocol constructs such as usernames and free-form appropriate for common application protocol constructs.
strings.
2. Define each PRECIS string class in terms of Unicode code points 2. Define each PRECIS string class in terms of Unicode code points
and their properties so that an algorithm can be used to and their properties so that an algorithm can be used to
determine whether each code point or character category is valid, determine whether each code point or character category is valid,
disallowed, or unassigned. contextual rule required, disallowed, or unassigned.
3. Define string classes in terms of allowable code points, so that 3. Define string classes in terms of allowable code points, so that
any code point not explicitly allowed is forbidden. any code point not explicitly allowed is forbidden.
4. Enable application protocols to subclass the PRECIS string 4. Enable application protocols to define profiles of the PRECIS
classes if needed, mainly to disallow particular code points that string classes, addressing matters such as width mapping, case
are currently disallowed in the relevant application protocol folding and other forms of character mapping, Unicode
(e.g., characters with special or reserved meaning, such as "@" normalization, directionality, and further excluded code points
and "/" when used as separators within identifiers). or character categories.
5. Leave various mapping operations (e.g., case preservation or
lowercasing, Unicode normalization, mapping of certain characters Whereas the string classes define the "baseline" code points for a
to other characters or to nothing, handling of full-width and range of applications, profiling enables application protocols to
half-width characters, handling of right-to-left characters) as further restrict the allowable code points beyond those specified for
the responsibility of application protocols, as was done for the relevant string class (e.g., characters with special or reserved
IDNA2008 through an IDNA-specific mapping document [RFC5895]. meaning, such as "@" and "/" when used as separators within
identifiers) and to apply the string classes in ways that are
appropriate for constructs such as usernames and passwords
[I-D.ietf-precis-saslprepbis], nicknames [I-D.ietf-precis-nickname],
the localparts of instant messaging addresses
[I-D.ietf-xmpp-6122bis], and free-form strings
[I-D.ietf-xmpp-6122bis]. Profiles are responsible for defining the
handling of right-to-left characters as well as various mapping
operations of the kind also discussed for IDNs in [RFC5895], such as
case preservation or lowercasing, Unicode normalization, mapping of
certain characters to other characters or to nothing, and mapping of
full-width and half-width characters.
It is expected that this framework will yield the following benefits: It is expected that this framework will yield the following benefits:
o Application protocols will be more version-agile with regard to o Application protocols will be more version-agile with regard to
the Unicode database. the Unicode database.
o Implementers will be able to share code point tables and software o Implementers will be able to share code point tables and software
code across application protocols, most likely by means of code across application protocols, most likely by means of
software libraries. software libraries.
o End users will be able to acquire more accurate expectations about o End users will be able to acquire more accurate expectations about
the code points that are acceptable in various contexts. Given the code points that are acceptable in various contexts. Given
this more uniform set of string classes, it is also expected that this more uniform set of string classes, it is also expected that
copy/paste operations between software implementing different copy/paste operations between software implementing different
application protocols will be more predictable and coherent. application protocols will be more predictable and coherent.
Although this framework is similar to IDNA2008 and borrows some of Although this framework is similar to IDNA2008 and borrows some of
the character categories defined in [RFC5892], it defines additional the character categories defined in [RFC5892], it defines additional
string classes and character categories to meet the needs of common character categories to meet the needs of common application
application protocols. protocols.
The character categories and calculation rules defined under
Section 7 and Section 8 are normative and apply to all Unicode code
points. The list of code points provided under Appendix A are non-
normative and merely show, for illustrative purposes, the
consequences of the character categories and calculation rules, and
the resulting property values.
2. Terminology 2. Terminology
Many important terms used in this document are defined in [RFC5890], Many important terms used in this document are defined in [RFC5890],
[RFC6365], [RFC6885], and [UNICODE]. [RFC6365], [RFC6885], and [UNICODE]. The terms "left-to-right" (LTR)
and "right-to-left" (RTL) are defined in [UAX9].
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in "OPTIONAL" in this document are to be interpreted as described in
[RFC2119]. [RFC2119].
3. String Classes 3. String Classes
3.1. Overview 3.1. Overview
skipping to change at page 7, line 5 skipping to change at page 6, line 22
domain name (IDN), although it does not use the term "string class". domain name (IDN), although it does not use the term "string class".
(This document does not define a string class for domain names, and (This document does not define a string class for domain names, and
application protocols are strongly encouraged to use IDNA2008 as the application protocols are strongly encouraged to use IDNA2008 as the
appropriate method to prepare domain names and hostnames.) Because appropriate method to prepare domain names and hostnames.) Because
the IDN string class is designed to meet the particular requirements the IDN string class is designed to meet the particular requirements
of the Domain Name System (DNS), additional string classes are needed of the Domain Name System (DNS), additional string classes are needed
for non-DNS applications. for non-DNS applications.
Starting in 2010, various "customers" of Stringprep began to discuss Starting in 2010, various "customers" of Stringprep began to discuss
the need to define a post-Stringprep approach to the preparation and the need to define a post-Stringprep approach to the preparation and
comparison of internationalized strings. As a result of analyzing comparison of internationalized strings other than IDNs. This
existing Stringprep profiles, this community concluded that most community analyzed the existing Stringprep profiles and also weighed
existing uses could be addressed by two string classes: the costs and benefits of defining a relatively small set of Unicode
characters that would minimize the potential for user confusion
caused by visually similar characters (and thus be relatively "safe")
vs. defining a much larger set of Unicode characters that would
maximize the potential for user expressiveness (and thus be
relatively inclusive). As a result, the community concluded that
most existing uses could be addressed by two string classes:
IdentifierClass: a sequence of letters, numbers, and symbols that is IdentifierClass: a sequence of letters, numbers, and some symbols
used to identify or address a network entity such as a user that is used to identify or address a network entity such as a
account, a venue (e.g., a chatroom), an information source (e.g., user account, a venue (e.g., a chatroom), an information source
a data feed), or a collection of data (e.g., a file); the intent (e.g., a data feed), or a collection of data (e.g., a file); the
is that this class will be very safe for use in a wide variety of intent is that this class will be very safe for use in a wide
application protocols, with the result that safety has been variety of application protocols, with the result that safety has
prioritized over inclusiveness for this class. been prioritized over inclusiveness for this class.
FreeformClass: a sequence of letters, numbers, symbols, spaces, and FreeformClass: a sequence of letters, numbers, symbols, spaces, and
other code points that is used for free-form strings, including other code points that is used for free-form strings, including
passwords as well as display elements such as human-friendly passwords as well as display elements such as human-friendly
nicknames in chatrooms; the intent is that this class will allow nicknames in chatrooms; the intent is that this class will allow
nearly any Unicode character, with the result that inclusiveness nearly any Unicode character, with the result that inclusiveness
has been prioritized over safety for this class (e.g., protocol has been prioritized over safety for this class (e.g., protocol
designers, application developers, service providers, and end designers, application developers, service providers, and end
users might not understand or be able to enter all of the users might not understand or be able to enter all of the
characters that can be included in the FreeformClass). characters that can be included in the FreeformClass).
Although members of the community discussed the possibility of Future specifications might define additional PRECIS string classes,
defining other PRECIS string classes (e.g., a class falling somewhere such as a class that falls somewhere between the IdentifierClass and
between the IdentifierClass and the FreeformClass), they concluded the FreeformClass. At this time, it is not clear how useful such a
that the IdentifierClass would be a safe choice meeting the needs of class would be. In any case, because application developers are able
many or even most application protocols, and that protocols needing a to define profiles of PRECIS string classes, a protocol needing a
wider range of Unicode characters could use the FreeformClass construct between the IdentiferClass and the FreeformClass could of
directly or subclass it if needed. course define a restricted profile of the FreeformClass if needed.
The following subsections discuss the IdentifierClass and The following subsections discuss the IdentifierClass and
FreeformClass in more detail, with reference to the dimensions FreeformClass in more detail, with reference to the dimensions
described in Section 3 of [RFC6885]. (Naturally, future documents described in Section 3 of [RFC6885]. (Naturally, future documents
can define PRECIS string classes beyond the IdentifierClass and can define PRECIS string classes beyond the IdentifierClass and
FreeformClass; see Section 10.2.) Each string class (or a particular FreeformClass; see Section 9.2.) Each string class is defined by the
usage thereof) is defined by the following behavioral rules: following behavioral rules:
Valid: defines which code points and character categories are Valid: Defines which code points and character categories are
treated as valid input to the string. treated as valid input to the string.
Disallowed: defines which code points and character categories are Contextual Rule Required: Defines which code points and character
treated as disallowed for the string. categories are treated as requiring a contextual rule (i.e.,
Unassigned: defines application behavior in the presence of code either CONTEXTJ or CONTEXTO).
Disallowed: Defines which code points and character categories need
to be excluded from the string.
Unassigned: Defines application behavior in the presence of code
points that are unassigned, i.e. unknown for the version of points that are unassigned, i.e. unknown for the version of
Unicode the application is built upon. Unicode the application is built upon.
Width Mapping: specifies if width mapping is performed on fullwidth This document defines the valid, contextual rule required,
and halfwidth characters, and how the mapping is done (e.g., disallowed, and unassigned rules for the IdentifierClass and
mapping fullwidth and halfwidth characters to their decomposition FreeformClass. As described under Section 4, profiles of these
equivalents). string classes are responsible for defining the width mapping,
Additional Mappings: specifies whether additional mappings are to be additional mapping, case mapping, normalization, directionality, and
applied, such as mapping of delimiter characters, mapping of exclusion rules.
special characters (e.g., non-ASCII space characters to ASCII
space or certain characters to nothing), and case mapping based on
language and local context (see [I-D.ietf-precis-mappings]).
Case Mapping: specifies if case mapping is performed (instead of
case preservation) on uppercase and titlecase characters, and how
the mapping is done (e.g., mapping uppercase and titlecase
characters to their lowercase equivalents).
Normalization: defines which Unicode normalization form (D, KD, C,
or KC) is to be applied (see [UAX15]).
Directionality: defines application behavior in the presence of code
points that have directionality, in particular right-to-left code
points as defined in the Unicode database (see [UAX9]).
This document defines the valid, disallowed, and unassigned rules for
the IdentifierClass and FreeformClass. Application protocols that
use these string classes are responsible for defining the
normalization, case mapping, width mapping, and directionality rules,
as well as any additional mappings to be applied
3.2. Order of Operations
To ensure proper comparison, the following order of operations is
REQUIRED:
1. Width mapping
2. Additional mappings as specified in [I-D.ietf-precis-mappings]:
1. Delimiter mapping
2. Special mapping
3. Local case mapping
3. Non-local case mapping
4. Normalization
5. PRECIS protocol
3.3. IdentifierClass 3.2. IdentifierClass
Most application technologies need strings that can be used to refer Most application technologies need strings that can be used to refer
to, include, or communicate protocol strings like usernames, file to, include, or communicate protocol strings like usernames, file
names, data feed identifiers, and chatroom names. We group such names, data feed identifiers, and chatroom names. We group such
strings into a class called "IdentifierClass" having the following strings into a class called "IdentifierClass" having the following
features. features.
3.3.1. Valid 3.2.1. Valid
o Code points traditionally used as letters and numbers in writing o Code points traditionally used as letters and numbers in writing
systems, i.e., the LetterDigits ("A") category first defined in systems, i.e., the LetterDigits ("A") category first defined in
[RFC5892] and listed here under Section 6.1. [RFC5892] and listed here under Section 7.1.
o Code points in the range U+0021 through U+007E, i.e., the o Code points in the range U+0021 through U+007E, i.e., the
(printable) ASCII7 ("K") rule defined under Section 6.11. These (printable) ASCII7 ("K") rule defined under Section 7.11. These
code points are "grandfathered" into PRECIS and thus are valid code points are "grandfathered" into PRECIS and thus are valid
even if they would otherwise be disallowed according to the even if they would otherwise be disallowed according to the
property-based rules specified in the next section. property-based rules specified in the next section.
Although the PRECIS IdentifierClass re-uses the LetterDigits category Although the PRECIS IdentifierClass re-uses the LetterDigits category
from IDNA2008, the range of characters allowed in the IdentifierClass from IDNA2008, the range of characters allowed in the IdentifierClass
is wider than the range of characters allowed in IDNA2008. The main is wider than the range of characters allowed in IDNA2008. The main
reason is that IDNA2008 applies the Unstable category before the reason is that IDNA2008 applies the Unstable category before the
LetterDigits category, thus disallowing uppercase characters, whereas LetterDigits category, thus disallowing uppercase characters, whereas
the IdentifierClass does not apply the Unstable category. the IdentifierClass does not apply the Unstable category.
3.3.2. Disallowed 3.2.2. Contextual Rule Required
o Certain characters from the Exceptions ("F") category defined
under Section 7.5.
o Joining characters, i.e., the JoinControl ("H") category defined
under Section 7.8.
3.2.3. Disallowed
o Control characters, i.e., the Controls ("L") category defined o Control characters, i.e., the Controls ("L") category defined
under Section 6.12. under Section 7.12.
o Ignorable characters, i.e., the PrecisIgnorableProperties ("M") o Ignorable characters, i.e., the PrecisIgnorableProperties ("M")
category defined under Section 6.13. category defined under Section 7.13.
o Space characters, i.e., the Spaces ("N") category defined under o Space characters, i.e., the Spaces ("N") category defined under
Section 6.14. Section 7.14.
o Symbol characters, i.e., the Symbols ("O") category defined under o Symbol characters, i.e., the Symbols ("O") category defined under
Section 6.15. Section 7.15.
o Punctuation characters, i.e., the Punctuation ("P") category o Punctuation characters, i.e., the Punctuation ("P") category
defined under Section 6.16. defined under Section 7.16.
o Any character that has a compatibility equivalent, i.e., the o Any character that has a compatibility equivalent, i.e., the
HasCompat ("Q") category defined under Section 6.17. These code HasCompat ("Q") category defined under Section 7.17. These code
points are disallowed even if they would otherwise be valid points are disallowed even if they would otherwise be valid
according to the property-based rules specified in the previous according to the property-based rules specified in the previous
section. section.
o Letters and digits other than the "traditional" letters and digits o Letters and digits other than the "traditional" letters and digits
allowed in IDNs, i.e., the OtherLetterDigits ("R") category allowed in IDNs, i.e., the OtherLetterDigits ("R") category
defined under Section 6.18. defined under Section 7.18.
3.3.3. Unassigned 3.2.4. Unassigned
Any code points that are not yet assigned in the Unicode character Any code points that are not yet designated in the Unicode character
set SHALL be considered Unassigned for purposes of the set SHALL be considered Unassigned for purposes of the
IdentifierClass. IdentifierClass, and a string containing such code points SHALL be
rejected.
3.3.4. Width Mapping
The width mapping rule MUST be specified by each application protocol
that uses or subclasses the IdentifierClass.
3.3.5. Additional Mappings
Additional mapping rules (if any) MUST be specified by each
application protocol that uses or subclasses the IdentifierClass (see
[I-D.ietf-precis-mappings]).
3.3.6. Case Mapping
The case mapping rule MUST be specified by each application protocol
that uses or subclasses the IdentifierClass.
3.3.7. Normalization
The Unicode normalization form MUST be specified by each application
protocol that uses or subclasses the IdentifierClass.
However, in accordance with [RFC5198], normalization form C (NFC) is
RECOMMENDED.
3.3.8. Directionality
The directionality rule MUST be specified by each application
protocol that uses or subclasses the IdentifierClass.
3.4. FreeformClass 3.3. FreeformClass
Some application technologies need strings that can be used in a Some application technologies need strings that can be used in a
free-form way, e.g., as a password in an authentication exchange (see free-form way, e.g., as a password in an authentication exchange (see
[I-D.ietf-precis-saslprepbis] or a nickname in a chatroom (see [I-D.ietf-precis-saslprepbis] or a nickname in a chatroom (see
[I-D.ietf-precis-nickname]). We group such things into a class [I-D.ietf-precis-nickname]). We group such things into a class
called "FreeformClass" having the following features. called "FreeformClass" having the following features.
Note: Consult Section 9.6 for relevant security considerations when Note: Consult Section 10.6 for relevant security considerations when
strings conforming to the FreeformClass, or a subclass thereof, are strings conforming to the FreeformClass, or a profile thereof, are
used as passwords. used as passwords.
3.4.1. Valid 3.3.1. Valid
o Traditional letters and numbers, i.e., the LetterDigits ("A") o Traditional letters and numbers, i.e., the LetterDigits ("A")
category first defined in [RFC5892] and listed here under category first defined in [RFC5892] and listed here under
Section 6.1. Section 7.1.
o Letters and digits other than the "traditional" letters and digits o Letters and digits other than the "traditional" letters and digits
allowed in IDNs, i.e., the OtherLetterDigits ("R") category allowed in IDNs, i.e., the OtherLetterDigits ("R") category
defined under Section 6.18. defined under Section 7.18.
o Code points in the range U+0021 through U+007E, i.e., the o Code points in the range U+0021 through U+007E, i.e., the
(printable) ASCII7 ("K") rule defined under Section 6.11. (printable) ASCII7 ("K") rule defined under Section 7.11.
o Any character that has a compatibility equivalent, i.e., the o Any character that has a compatibility equivalent, i.e., the
HasCompat ("Q") category defined under Section 6.17. HasCompat ("Q") category defined under Section 7.17.
o Space characters, i.e., the Spaces ("N") category defined under o Space characters, i.e., the Spaces ("N") category defined under
Section 6.14. Section 7.14.
o Symbol characters, i.e., the Symbols ("O") category defined under o Symbol characters, i.e., the Symbols ("O") category defined under
Section 6.15. Section 7.15.
o Punctuation characters, i.e., the Punctuation ("P") category o Punctuation characters, i.e., the Punctuation ("P") category
defined under Section 6.16. defined under Section 7.16.
3.4.2. Disallowed 3.3.2. Contextual Rule Required
o Certain characters from the Exceptions ("F") category defined
under Section 7.5.
o Joining characters, i.e., the JoinControl ("H") category defined
under Section 7.8.
3.3.3. Disallowed
o Control characters, i.e., the Controls ("L") category defined o Control characters, i.e., the Controls ("L") category defined
under Section 6.12. under Section 7.12.
o Ignorable characters, i.e., the PrecisIgnorableProperties ("M") o Ignorable characters, i.e., the PrecisIgnorableProperties ("M")
category defined under Section 6.13. category defined under Section 7.13.
3.4.3. Unassigned 3.3.4. Unassigned
Any code points that are not yet assigned in the Unicode character Any code points that are not yet designated in the Unicode character
set SHALL be considered Unassigned for purposes of the FreeformClass. set SHALL be considered Unassigned for purposes of the FreeformClass,
and a string containing such code points SHALL be rejected.
3.4.4. Width Mapping 4. Profiles
The width mapping rule MUST be specified by each application protocol 4.1. Principles
that uses or subclasses the FreeformClass.
Because one aspect of Unicode normalization form KC is width mapping, This framework document defines the valid, contextual-rule-required,
a PRECIS usage or subclass that uses NFKC does not need to specify disallowed, and unassigned rules for the IdentifierClass and the
width mapping. However, if NFC is used then the usage or subclass FreeformClass. A profile of a PRECIS string class MUST define the
needs to specify whether to apply width mapping; in this case, width width mapping, additional mapping (if any), case mapping,
mapping is in general RECOMMENDED because allowing fullwidth and normalization, directionality, and exclusion rules. A profile MAY
halfwidth characters to remain unmapped to their decomposition also restrict the allowable characters above and beyond the
equivalents would violate the principle of least user surprise. For definition of the relevant PRECIS string class (but MUST NOT add as
more information about the concept of width in East Asian scripts valid any code points or character categories that are disallowed by
within Unicode, see for instance [UAX11]. the relevant PRECIS string class). These matters are discussed in
the following subsections.
3.4.5. Additional Mappings Profiles of the PRECIS string classes MUST register with the IANA as
described under Section 9.3. It is RECOMMENDED for profile names to
be of the form "ProfilenameBaseClass", where the "Profilename" string
is a differentiator and "BaseClass" is the name of the PRECIS string
class being profiled; for example, the profile of the IdentifierClass
used for localparts of Jabber IDs in the Extensible Messaging and
Presence Protocol (XMPP) is named "JIDlocalIdentifierClass"
[I-D.ietf-xmpp-6122bis].
Additional mapping rules (if any) MUST be specified by each 4.1.1. Width Mapping
application protocol that uses or subclasses the FreeformClass (see
The width mapping rule of a profile specifies whether width mapping
is performed on fullwidth and halfwidth characters, and how the
mapping is done (e.g., mapping fullwidth and halfwidth characters to
their decomposition equivalents).
The normalization form specified by a profile (see below) has an
impact on the need for width mapping. Because one aspect of Unicode
normalization form KC (NFKC) is width mapping, a profile that uses
NFKC does not need to specify width mapping. However, if Unicode
normalization form C (NFC) is used then the profile needs to specify
whether to apply width mapping; in this case, width mapping is in
general RECOMMENDED because allowing fullwidth and halfwidth
characters to remain unmapped to their decomposition equivalents
would violate the principle of least user surprise. For more
information about the concept of width in East Asian scripts within
Unicode, see for instance [UAX11].
4.1.2. Additional Mappings
The additional mappings rule of a profile specifies whether
additional mappings are to be applied, such as mapping of delimiter
characters, mapping of special characters (e.g., non-ASCII space
characters to ASCII space or certain characters to nothing), and case
mapping based on language and local context (see
[I-D.ietf-precis-mappings]). [I-D.ietf-precis-mappings]).
3.4.6. Case Mapping 4.1.3. Case Mapping
The case mapping rule MUST be specified by each application protocol The case mapping rule of a profile specifies whether case mapping is
that uses or subclasses the FreeformClass. performed (instead of case preservation) on uppercase and titlecase
characters, and how the mapping is done (e.g., mapping uppercase and
titlecase characters to their lowercase equivalents).
Use of the Unicode Default Case Folding algorithm is RECOMMENDED.
In general, the combination of case preservation and case-insensitive In general, the combination of case preservation and case-insensitive
comparison of internationalized strings is NOT RECOMMENDED; instead, comparison of internationalized strings is NOT RECOMMENDED; instead,
application protocols SHOULD either (a) not preserve case but perform application protocols SHOULD either (a) not preserve case but perform
case-insensitive comparison or (b) preserve case but perform case- case-insensitive comparison or (b) preserve case but perform case-
sensitive comparison. sensitive comparison.
In order to maximize entropy and minimize the potential for false In order to maximize entropy and minimize the potential for false
positives, it is NOT RECOMMENDED for application protocols to map positives, it is NOT RECOMMENDED for application protocols to map
uppercase and titlecase code points to their lowercase equivalents uppercase and titlecase code points to their lowercase equivalents
when strings conforming to the FreeformClass, or a subclass thereof, when strings conforming to the FreeformClass, or a profile thereof,
are used in passwords; instead, it is RECOMMENDED to preserve the are used in passwords; instead, it is RECOMMENDED to preserve the
case of all code points contained in such strings and then perform case of all code points contained in such strings and then perform
case-sensitive comparison. See also the related discussion in case-sensitive comparison. See also the related discussion in
[I-D.ietf-precis-saslprepbis]. [I-D.ietf-precis-saslprepbis].
3.4.7. Normalization 4.1.4. Normalization
The Unicode normalization form MUST be specified by each application The normalization rule of a profile specifies which Unicode
protocol that uses or subclasses the FreeformClass. normalization form (D, KD, C, or KC) is to be applied (see [UAX15]
for background information).
However, in accordance with [RFC5198], normalization form C (NFC) is In accordance with [RFC5198], normalization form C (NFC) is
RECOMMENDED. RECOMMENDED.
3.4.8. Directionality 4.1.5. Directionality
The directionality rule MUST be specified by each application
protocol that uses or subclasses the FreeformClass.
4. Use of PRECIS String Classes
4.1. Principles
This document defines the valid, disallowed, and unassigned rules.
Application protocols that use the PRECIS string classes MUST define
the width mapping, additional mapping (if any), case mapping,
normalization, and directionality rules. That is, such definitions
MUST at a minimum specify the following:
Width Mapping: Whether fullwidth and halfwidth code points are to be The directionality rule of a profile specifies which strings are to
mapped to their decomposition equivalents. be considered left-to-right (LTR) and right-to-left (RTL), and the
Additional Mappings: Whether additional mappings are to be applied, allowable sequences of characters in LTR and RTL strings (see
such as mapping of delimiter characters, mapping of special [UAX9]); note that mixed-direction strings are not supported, since
characters (e.g., non-ASCII space characters to ASCII space or there is currently no widely accepted and implemented solution for
certain characters to nothing), and case mapping based on language the processing and display of mixed-direction strings. Possible
and local context (see [I-D.ietf-precis-mappings]). rules include, but are not limited to, (a) considering any string
Case Mapping: Whether uppercase and titlecase code points are to be that contains a right-to-left code point to be a right-to-left
(a) preserved or (b) mapped to lowercase. string, or (b) applying the "Bidi Rule" from [RFC5893].
Normalization: Which Unicode normalization form (D, KD, C, or KC) is
to be applied (see [UAX15] for background information); in
accordance with [RFC5198], NFC is RECOMMENDED.
Directionality: Whether any instance of the class that contains a
right-to-left code point is to be considered a right-to-left
string, or whether some other rule is to be applied (e.g., the
"Bidi Rule" from [RFC5893]).
4.2. Subclassing 4.1.6. Exclusions
Application protocols are allowed to subclass the PRECIS string The exclusions rule of a profile specifies whether the profile
classes specified in this document. As the word "subclass" implies, excludes additional code points or character categories above and
a subclass MUST NOT add as valid any code points or character beyond those excluded by the string class being profiled. That is, a
categories that are disallowed by the relevant PRECIS string class. profile MAY do either of the following:
However, a subclass MAY do either of the following:
1. Exclude specific code points that are included in the relevant 1. Exclude specific code points that are allowed by the relevant
PRECIS string class. string class.
2. Exclude characters matching certain Unicode properties (e.g., 2. Exclude characters matching certain Unicode properties (e.g.,
math symbols) that are included in the relevant PRECIS string math symbols) that are included in the relevant PRECIS string
class. class.
As a result, code points that are defined as valid for the PRECIS As a result of such exclusions, code points that are defined as valid
string class being subclassed will be defined as disallowed for the for the PRECIS string class being profiled will be defined as
subclass. disallowed for the profile.
Application protocols that subclass the PRECIS string classes MUST
register with the IANA as described under Section 10.3.
It is RECOMMENDED for subclass names to be of the form
"SubclassBaseClass", where the "Subclass" string is a differentiator
and "BaseClass" is the name of the PRECIS string class being
subclassed; for example, the subclass of the IdentifierClass used for
localparts in the Extensible Messaging and Presence Protocol (XMPP)
is named "LocalpartIdentifierClass" [I-D.ietf-xmpp-6122bis].
4.3. Building Application-Layer Constructs 4.2. Building Application-Layer Constructs
Sometimes, an application-layer construct does not map directly to Sometimes, an application-layer construct does not map in a
one of the PRECIS string classes. Consider, for example, the "simple straightforward manner to one of the PRECIS string classes or a
user name" construct in the Simple Authentication and Security Layer profile thereof. Consider, for example, the "simple user name"
(SASL) [RFC4422]. Depending on the deployment, a simple user name construct in the Simple Authentication and Security Layer (SASL)
might take the form of a user's full name (e.g., the user's personal [RFC4422]. Depending on the deployment, a simple user name might
name followed by a space and then the user's family name). Such a take the form of a user's full name (e.g., the user's personal name
simple user name cannot be defined as an instance of the followed by a space and then the user's family name). Such a simple
IdentifierClass, since space characters are not allowed in the user name cannot be defined as an instance of the IdentifierClass or
a profile thereof, since space characters are not allowed in the
IdentifierClass; however, it could be defined using a space-separated IdentifierClass; however, it could be defined using a space-separated
sequence of IdentifierClass instances, as in the following pseudo- sequence of IdentifierClass instances, as in the following pseudo-
ABNF [RFC5234]: ABNF [RFC5234]:
fullname = namepart [1*(1*SP namepart)] fullname = namepart [1*(1*SP namepart)]
namepart = 1*(idpoint) namepart = 1*(idpoint)
; ;
; an "idpoint" is a UTF-8 encoded Unicode code point ; an "idpoint" is a UTF-8 encoded Unicode code point
; that conforms to the PRECIS IdentifierClass ; that conforms to the PRECIS IdentifierClass
Similar techniques could be used to define many application-layer Similar techniques could be used to define many application-layer
constructs, say of the form "user@domain" or "/path/to/file". constructs, say of the form "user@domain" or "/path/to/file".
4.4. A Note about Spaces 4.3. A Note about Spaces
With regard to the IdentiferClass, the consensus of the PRECIS With regard to the IdentiferClass, the consensus of the PRECIS
Working Group was that spaces are problematic for many reasons, Working Group was that spaces are problematic for many reasons,
including: including:
o Many Unicode characters are confusable with ASCII space. o Many Unicode characters are confusable with ASCII space.
o Even if non-ASCII space characters are mapped to ASCII space o Even if non-ASCII space characters are mapped to ASCII space
(U+0020), space characters are often not rendered in user (U+0020), space characters are often not rendered in user
interfaces, leading to the possibility that human user might interfaces, leading to the possibility that human user might
consider a string containing spaces to be equivalent to the same consider a string containing spaces to be equivalent to the same
skipping to change at page 15, line 4 skipping to change at page 13, line 24
One consequence of disallowing space characters in the One consequence of disallowing space characters in the
IdentifierClass might be to effectively discourage the use of ASCII IdentifierClass might be to effectively discourage the use of ASCII
space (or, even more problematically, non-ASCII space characters) space (or, even more problematically, non-ASCII space characters)
within identifiers created in newer application protocols; given the within identifiers created in newer application protocols; given the
challenges involved in properly handling space characters in challenges involved in properly handling space characters in
identifiers and other protocol strings, the Working Group considered identifiers and other protocol strings, the Working Group considered
this to be a feature, not a bug. this to be a feature, not a bug.
However, the FreeformClass does allow spaces, which enables However, the FreeformClass does allow spaces, which enables
application protocols to define subclasses of the FreeformClass that application protocols to define profiles of the FreeformClass that
are more flexible than any profiles of the IdentifierClass. are more flexible than any profiles of the IdentifierClass.
5. Code Point Properties 5. Order of Operations
To ensure proper comparison, the following order of operations is
REQUIRED:
1. Width mapping
2. Additional mappings as specified in [I-D.ietf-precis-mappings]:
1. Delimiter mapping
2. Special mapping
3. Local case mapping
3. Non-local case mapping
4. Normalization
5. Behavioral rules for determining whether a code point is valid,
allowed under a contextual rule, disallowed, or unassigned
As already described, the width mapping, additional mapping, non-
local case mapping, and normalization operations are specified for
each profile, whereas the behavioral rules are specified for each
string class. Some of the logic behind this order is provided under
Section 4.1.1 and in [I-D.ietf-precis-mappings].
6. Code Point Properties
In order to implement the string classes described above, this In order to implement the string classes described above, this
document does the following: document does the following:
1. Reviews and classifies the collections of code points in the 1. Reviews and classifies the collections of code points in the
Unicode character set by examining various code point properties. Unicode character set by examining various code point properties.
2. Defines an algorithm for determining a derived property value, 2. Defines an algorithm for determining a derived property value,
which can vary depending on the string class being used by the which can vary depending on the string class being used by the
relevant application protocol. relevant application protocol.
This document is not intended to specify precisely how derived This document is not intended to specify precisely how derived
property values are to be applied in protocol strings. That property values are to be applied in protocol strings. That
information is the responsibility of the protocol specification that information is the responsibility of the protocol specification that
uses or subclasses a PRECIS string class from this document. uses or profiles a PRECIS string class from this document.
The value of the property is to be interpreted as follows. The value of the property is to be interpreted as follows.
PROTOCOL VALID Those code points that are allowed to be used in any PROTOCOL VALID Those code points that are allowed to be used in any
PRECIS string class (IdentifierClass and FreeformClass). Code PRECIS string class (IdentifierClass and FreeformClass). Code
points with this property value are permitted for general use in points with this property value are permitted for general use in
any string class. The abbreviated term PVALID is used to refer to any string class. The abbreviated term PVALID is used to refer to
this value in the remainder of this document. this value in the remainder of this document.
SPECIFIC CLASS PROTOCOL VALID Those code points that are allowed to SPECIFIC CLASS PROTOCOL VALID Those code points that are allowed to
be used in specific string classes. Code points with this be used in specific string classes. Code points with this
property value are permitted for use in specific string classes. property value are permitted for use in specific string classes.
In the remainder of this document, the abbreviated term *_PVAL is In the remainder of this document, the abbreviated term *_PVAL is
used, where * = (NAME | FREE), i.e., either FREE_PVAL or ID_PVAL. used, where * = (ID | FREE), i.e., either FREE_PVAL or ID_PVAL.
CONTEXTUAL RULE REQUIRED Some characteristics of the character, such CONTEXTUAL RULE REQUIRED Some characteristics of the character, such
as its being invisible in certain contexts or problematic in as its being invisible in certain contexts or problematic in
others, require that it not be used in labels unless specific others, require that it not be used in labels unless specific
other characters or properties are present. The abbreviated term other characters or properties are present. The abbreviated term
CONTEXT is used to refer to this value in the remainder of this CONTEXT is used to refer to this value in the remainder of this
document. As in IDNA2008, there are two subdivisions of document. As in IDNA2008, there are two subdivisions of
CONTEXTUAL RULE REQUIRED, the first for Join_controls (called CONTEXTUAL RULE REQUIRED, the first for Join_controls (called
CONTEXTJ) and the second for other characters (called CONTEXTO). CONTEXTJ) and the second for other characters (called CONTEXTO).
A character with the derived property value CONTEXTJ or CONTEXTO
(CONTEXTUAL RULE REQUIRED) MUST NOT be used unless an appropriate
rule has been established and the context of the character is
consistent with that rule.
DISALLOWED Those code points that must not permitted in any PRECIS DISALLOWED Those code points that must not permitted in any PRECIS
string class. string class.
SPECIFIC CLASS DISALLOWED Those code points that are not to be SPECIFIC CLASS DISALLOWED Those code points that are not to be
included in a specific string class. Code points with this included in a specific string class. Code points with this
property value are not permitted in one of the string classes but property value are not permitted in one of the string classes but
might be permitted in others. In the remainder of this document, might be permitted in others. In the remainder of this document,
the abbreviated term *_DIS is used, where * = (NAME | FREE), i.e., the abbreviated term *_DIS is used, where * = (ID | FREE), i.e.,
either FREE_DIS or ID_DIS. either FREE_DIS or ID_DIS.
UNASSIGNED Those code points that are not designated (i.e. are UNASSIGNED Those code points that are not designated (i.e. are
unassigned) in the Unicode Standard. unassigned) in the Unicode Standard.
The mechanisms described here allow determination of the value of the The mechanisms described here allow determination of the value of the
property for future versions of Unicode (including characters added property for future versions of Unicode (including characters added
after Unicode 5.2 or 6.1 depending on the category, since some after Unicode 5.2 or 6.2 depending on the category, since some
categories in this document are reused from IDNA2008 and therefore categories in this document are reused from IDNA2008 and therefore
were defined at the time of Unicode 5.2). Changes in Unicode were defined at the time of Unicode 5.2). Changes in Unicode
properties that do not affect the outcome of this process do not properties that do not affect the outcome of this process do not
affect this framework. For example, a character can have its Unicode affect this framework. For example, a character can have its Unicode
General_Category value [UNICODE] change from So to Sm, or from Lo to General_Category value [UNICODE] change from So to Sm, or from Lo to
Ll, without affecting the algorithm results. Moreover, even if such Ll, without affecting the algorithm results. Moreover, even if such
changes were to result, the BackwardCompatible list (Section 6.7) can changes were to result, the BackwardCompatible list (Section 7.7) can
be adjusted to ensure the stability of the results. be adjusted to ensure the stability of the results.
Some code points need to be allowed in exceptional circumstances, but Some code points need to be allowed in exceptional circumstances, but
ought to be excluded in all other cases; these rules are also ought to be excluded in all other cases; these rules are also
described in other documents. The most notable of these are the Join described in other documents. The most notable of these are the Join
Control characters, U+200D ZERO WIDTH JOINER and U+200C ZERO WIDTH Control characters, U+200D ZERO WIDTH JOINER and U+200C ZERO WIDTH
NON-JOINER. Both of them have the derived property value CONTEXTJ. NON-JOINER. Both of them have the derived property value CONTEXTJ.
A character with the derived property value CONTEXTJ or CONTEXTO A character with the derived property value CONTEXTJ or CONTEXTO
(CONTEXTUAL RULE REQUIRED) is not to be used unless an appropriate (CONTEXTUAL RULE REQUIRED) is not to be used unless an appropriate
rule has been established and the context of the character is rule has been established and the context of the character is
consistent with that rule. It is invalid to generate a string consistent with that rule. It is invalid to generate a string
containing these characters unless such a contextual rule is found containing these characters unless such a contextual rule is found
and satisfied. PRECIS does not define its own contextual rules, but and satisfied. PRECIS does not define its own contextual rules, but
instead re-uses the contextual rules defined for IDNA2008; please see instead re-uses the contextual rules defined for IDNA2008; please see
Appendix A of [RFC5892] for more information. Appendix A of [RFC5892] for more information.
6. Category Definitions Used to Calculate Derived Property Value 7. Category Definitions Used to Calculate Derived Property
The derived property obtains its value based on a two-step procedure: The derived property obtains its value based on a two-step procedure:
1. Characters are placed in one or more character categories either 1. Characters are placed in one or more character categories either
(1) based on core properties defined by the Unicode Standard or (1) based on core properties defined by the Unicode Standard or
(2) by treating the code point as an exception and addressing the (2) by treating the code point as an exception and addressing the
code point based on its code point value. These categories are code point based on its code point value. These categories are
not mutually exclusive. not mutually exclusive.
2. Set operations are used with these categories to determine the 2. Set operations are used with these categories to determine the
values for a property that is specific to a given string class. values for a property that is specific to a given string class.
These operations are specified under Section 7. These operations are specified under Section 8.
(Note: Unicode property names and property value names might have (Note: Unicode property names and property value names might have
short abbreviations, such as "gc" for the General_Category property short abbreviations, such as "gc" for the General_Category property
and "Ll" for the Lowercase_Letter property value of the gc property.) and "Ll" for the Lowercase_Letter property value of the gc property.)
In the following specification of character categories, the operation In the following specification of character categories, the operation
that returns the value of a particular Unicode character property for that returns the value of a particular Unicode character property for
a code point is designated by using the formal name of that property a code point is designated by using the formal name of that property
(from the Unicode PropertyAliases.txt [1]) followed by '(cp)' for (from the Unicode PropertyAliases.txt [1]) followed by '(cp)' for
"code point". For example, the value of the General_Category "code point". For example, the value of the General_Category
property for a code point is indicated by General_Category(cp). property for a code point is indicated by General_Category(cp).
The first ten categories (A-J) shown below were previously defined The first ten categories (A-J) shown below were previously defined
for IDNA2008 and are copied directly from [RFC5892]. Some of these for IDNA2008 and are copied directly from [RFC5892]. Some of these
categories are reused in PRECIS and some of them are not; however, categories are reused in PRECIS and some of them are not; however,
the lettering of categories is retained to prevent overlap and to the lettering of categories is retained to prevent overlap and to
ease implementation of both IDNA2008 and PRECIS in a single software ease implementation of both IDNA2008 and PRECIS in a single software
application. The next seven categories (K-Q) are specific to PRECIS. application. The next eight categories (K-R) are specific to PRECIS.
6.1. LetterDigits (A) 7.1. LetterDigits (A)
Note: This category is defined in [RFC5892] and copied here for use Note: This category is defined in [RFC5892] and copied here for use
in PRECIS. in PRECIS.
A: General_Category(cp) is in {Ll, Lu, Lm, Lo, Mn, Mc, Nd} A: General_Category(cp) is in {Ll, Lu, Lm, Lo, Mn, Mc, Nd}
These rules identify characters commonly used in mnemonics and often These rules identify characters commonly used in mnemonics and often
informally described as "language characters". informally described as "language characters".
For more information, see section 4.5 of [UNICODE]. For more information, see section 4.5 of [UNICODE].
The categories used in this rule are: The categories used in this rule are:
o Ll - Lowercase_Letter o Ll - Lowercase_Letter
o Lu - Uppercase_Letter o Lu - Uppercase_Letter
o Lm - Modifier_Letter o Lm - Modifier_Letter
o Lo - Other_Letter o Lo - Other_Letter
o Mn - Nonspacing_Mark o Mn - Nonspacing_Mark
o Mc - Spacing_Mark o Mc - Spacing_Mark
o Nd - Decimal_Number o Nd - Decimal_Number
6.2. Unstable (B) 7.2. Unstable (B)
Note: This category is defined in [RFC5892] but not used in PRECIS. Note: This category is defined in [RFC5892] but not used in PRECIS.
6.3. IgnorableProperties (C) 7.3. IgnorableProperties (C)
Note: This category is defined in [RFC5892] but not used in PRECIS. Note: This category is defined in [RFC5892] but not used in PRECIS.
See the "PrecisIgnorableProperties (M)" category below for a more See the "PrecisIgnorableProperties (M)" category below for a more
inclusive category used in PRECIS identifiers. inclusive category used in PRECIS identifiers.
6.4. IgnorableBlocks (D) 7.4. IgnorableBlocks (D)
Note: This category is defined in [RFC5892] but not used in PRECIS. Note: This category is defined in [RFC5892] but not used in PRECIS.
6.5. LDH (E) 7.5. LDH (E)
Note: This category is defined in [RFC5892] but not used in PRECIS. Note: This category is defined in [RFC5892] but not used in PRECIS.
See the "ASCII7 (K)" category below for a more inclusive category See the "ASCII7 (K)" category below for a more inclusive category
used in PRECIS identifiers. used in PRECIS identifiers.
6.6. Exceptions (F) 7.6. Exceptions (F)
Note: This category is defined in [RFC5892] and used in PRECIS to Note: This category is defined in [RFC5892] and used in PRECIS to
ensure consistent treatment of the relevant code points. ensure consistent treatment of the relevant code points.
F: cp is in {00B7, 00DF, 0375, 03C2, 05F3, 05F4, 0640, 0660, F: cp is in {00B7, 00DF, 0375, 03C2, 05F3, 05F4, 0640, 0660,
0661, 0662, 0663, 0664, 0665, 0666, 0667, 0668, 0661, 0662, 0663, 0664, 0665, 0666, 0667, 0668,
0669, 06F0, 06F1, 06F2, 06F3, 06F4, 06F5, 06F6, 0669, 06F0, 06F1, 06F2, 06F3, 06F4, 06F5, 06F6,
06F7, 06F8, 06F9, 06FD, 06FE, 07FA, 0F0B, 3007, 06F7, 06F8, 06F9, 06FD, 06FE, 07FA, 0F0B, 3007,
302E, 302F, 3031, 3032, 3033, 3034, 3035, 303B, 302E, 302F, 3031, 3032, 3033, 3034, 3035, 303B,
30FB} 30FB}
skipping to change at page 19, line 32 skipping to change at page 18, line 32
302E; DISALLOWED # HANGUL SINGLE DOT TONE MARK 302E; DISALLOWED # HANGUL SINGLE DOT TONE MARK
302F; DISALLOWED # HANGUL DOUBLE DOT TONE MARK 302F; DISALLOWED # HANGUL DOUBLE DOT TONE MARK
3031; DISALLOWED # VERTICAL KANA REPEAT MARK 3031; DISALLOWED # VERTICAL KANA REPEAT MARK
3032; DISALLOWED # VERTICAL KANA REPEAT WITH VOICED SOUND MARK 3032; DISALLOWED # VERTICAL KANA REPEAT WITH VOICED SOUND MARK
3033; DISALLOWED # VERTICAL KANA REPEAT MARK UPPER HALF 3033; DISALLOWED # VERTICAL KANA REPEAT MARK UPPER HALF
3034; DISALLOWED # VERTICAL KANA REPEAT WITH VOICED SOUND MARK 3034; DISALLOWED # VERTICAL KANA REPEAT WITH VOICED SOUND MARK
UPPER HA UPPER HA
3035; DISALLOWED # VERTICAL KANA REPEAT MARK LOWER HALF 3035; DISALLOWED # VERTICAL KANA REPEAT MARK LOWER HALF
303B; DISALLOWED # VERTICAL IDEOGRAPHIC ITERATION MARK 303B; DISALLOWED # VERTICAL IDEOGRAPHIC ITERATION MARK
6.7. BackwardCompatible (G) 7.7. BackwardCompatible (G)
Note: This category is defined in [RFC5892] and copied here for use Note: This category is defined in [RFC5892] and copied here for use
in PRECIS. Because of how the PRECIS string classes are defined, in PRECIS. Because of how the PRECIS string classes are defined,
only changes that would result in code points being added to or only changes that would result in code points being added to or
removed from the LetterDigits ("A") category would result in removed from the LetterDigits ("A") category would result in
backward-incompatible modifications to code point assignments. backward-incompatible modifications to code point assignments.
Therefore, management of this category is handled via the processes Therefore, management of this category is handled via the processes
specified in [RFC5892]. specified in [RFC5892].
G: cp is in {} G: cp is in {}
This category includes the code points for which property values in This category includes the code points for which property values in
versions of Unicode after 5.2 have changed in such a way that the versions of Unicode after 5.2 have changed in such a way that the
derived property value would no longer be PVALID or DISALLOWED. If derived property value would no longer be PVALID or DISALLOWED. If
changes are made to future versions of Unicode so that code points changes are made to future versions of Unicode so that code points
might change property value from PVALID or DISALLOWED, then this might change property value from PVALID or DISALLOWED, then this
table can be updated and keep special exception values so that the table can be updated and keep special exception values so that the
property values for code points stay stable. property values for code points stay stable.
6.8. JoinControl (H) 7.8. JoinControl (H)
Note: This category is defined in [RFC5892] and copied here for use Note: This category is defined in [RFC5892] and copied here for use
in PRECIS. in PRECIS.
H: Join_Control(cp) = True H: Join_Control(cp) = True
This category consists of Join Control characters (i.e., they are not This category consists of Join Control characters (i.e., they are not
in LetterDigits (Section 6.1) but are still required in strings under in LetterDigits (Section 7.1) but are still required in strings under
some circumstances). some circumstances).
6.9. OldHangulJamo (I) 7.9. OldHangulJamo (I)
Note: This category is defined in [RFC5892] and copied here for use Note: This category is defined in [RFC5892] and copied here for use
in PRECIS. in PRECIS.
I: Hangul_Syllable_Type(cp) is in {L, V, T} I: Hangul_Syllable_Type(cp) is in {L, V, T}
This category consists of all conjoining Hangul Jamo (Leading Jamo, This category consists of all conjoining Hangul Jamo (Leading Jamo,
Vowel Jamo, and Trailing Jamo). Vowel Jamo, and Trailing Jamo).
Elimination of conjoining Hangul Jamos from the set of PVALID Elimination of conjoining Hangul Jamos from the set of PVALID
characters results in restricting the set of Korean PVALID characters characters results in restricting the set of Korean PVALID characters
just to preformed, modern Hangul syllable characters. Old Hangul just to preformed, modern Hangul syllable characters. Old Hangul
syllables, which must be spelled with sequences of conjoining Hangul syllables, which must be spelled with sequences of conjoining Hangul
Jamos, are not PVALID for string classes. Jamos, are not PVALID for string classes.
6.10. Unassigned (J) 7.10. Unassigned (J)
Note: This category is defined in [RFC5892] and copied here for use Note: This category is defined in [RFC5892] and copied here for use
in PRECIS. in PRECIS.
J: General_Category(cp) is in {Cn} and J: General_Category(cp) is in {Cn} and
Noncharacter_Code_Point(cp) = False Noncharacter_Code_Point(cp) = False
This category consists of code points in the Unicode character set This category consists of code points in the Unicode character set
that are not (yet) assigned. It should be noted that Unicode that are not (yet) designated. It should be noted that Unicode
distinguishes between 'unassigned code points' and 'unassigned distinguishes between 'unassigned code points' and 'unassigned
characters'. The unassigned code points are all but (Cn - characters'. The unassigned code points are all but (Cn -
Noncharacters), while the unassigned *characters* are all but (Cn + Noncharacters), while the unassigned characters are all but (Cn +
Cs). Cs).
6.11. ASCII7 (K) 7.11. ASCII7 (K)
This PRECIS-specific category exempts most characters in the This PRECIS-specific category exempts most characters in the
(printable) ASCII-7 range from other rules that might be applied (printable) ASCII-7 range from other rules that might be applied
during PRECIS processing, on the assumption that these code points during PRECIS processing, on the assumption that these code points
are in such wide use that disallowing them would be counter- are in such wide use that disallowing them would be counter-
productive. productive.
K: cp is in {0021..007E} K: cp is in {0021..007E}
6.12. Controls (L) 7.12. Controls (L)
L: Control(cp) = True L: Control(cp) = True
6.13. PrecisIgnorableProperties (M) 7.13. PrecisIgnorableProperties (M)
This PRECIS-specific category is used to group code points that are This PRECIS-specific category is used to group code points that are
not recommended for use in PRECIS string classes. not recommended for use in PRECIS string classes.
M: Default_Ignorable_Code_Point(cp) = True or M: Default_Ignorable_Code_Point(cp) = True or
Noncharacter_Code_Point(cp) = True Noncharacter_Code_Point(cp) = True
The definition for Default_Ignorable_Code_Point can be found in the The definition for Default_Ignorable_Code_Point can be found in the
DerivedCoreProperties.txt [2] file, and at the time of Unicode 6.1 is DerivedCoreProperties.txt [2] file, and at the time of Unicode 6.2 is
as follows: as follows:
Other_Default_Ignorable_Code_Point Other_Default_Ignorable_Code_Point
+ Cf (Format characters) + Cf (Format characters)
+ Variation_Selector + Variation_Selector
- White_Space - White_Space
- FFF9..FFFB (Annotation Characters) - FFF9..FFFB (Annotation Characters)
- 0600..0604, 06DD, 070F, 110BD (exceptional Cf characters - 0600..0604, 06DD, 070F, 110BD (exceptional Cf characters
that should be visible) that should be visible)
6.14. Spaces (N) 7.14. Spaces (N)
This PRECIS-specific category is used to group code points that are This PRECIS-specific category is used to group code points that are
space characters. space characters.
N: General_Category(cp) is in {Zs} N: General_Category(cp) is in {Zs}
6.15. Symbols (O) 7.15. Symbols (O)
This PRECIS-specific category is used to group code points that are This PRECIS-specific category is used to group code points that are
symbols. symbols.
O: General_Category(cp) is in {Sm, Sc, Sk, So} O: General_Category(cp) is in {Sm, Sc, Sk, So}
6.16. Punctuation (P) 7.16. Punctuation (P)
This PRECIS-specific category is used to group code points that are This PRECIS-specific category is used to group code points that are
punctuation characters. punctuation characters.
P: General_Category(cp) is in {Pc, Pd, Ps, Pe, Pi, Pf, Po} P: General_Category(cp) is in {Pc, Pd, Ps, Pe, Pi, Pf, Po}
6.17. HasCompat (Q) 7.17. HasCompat (Q)
This PRECIS-specific category is used to group code points that have This PRECIS-specific category is used to group code points that have
compatibility equivalents as explained in Chapter 2 and Chapter 3 of compatibility equivalents as explained in Chapter 2 and Chapter 3 of
[UNICODE]. [UNICODE].
Q: toNFKC(cp) != cp Q: toNFKC(cp) != cp
The toNFKC() operation returns the code point in normalization form The toNFKC() operation returns the code point in normalization form
KC. For more information, see Section 5 of [UAX15]. KC. For more information, see Section 5 of [UAX15].
6.18. OtherLetterDigits (R) 7.18. OtherLetterDigits (R)
This PRECIS-specific category is used to group code points that are This PRECIS-specific category is used to group code points that are
letters and digits other than the "traditional" letters and digits letters and digits other than the "traditional" letters and digits
grouped under the LetterDigits (A) class (see Section 6.1). grouped under the LetterDigits (A) class (see Section 7.1).
R: General_Category(cp) is in {Lt, Nl, No, Me} R: General_Category(cp) is in {Lt, Nl, No, Me}
7. Calculation of the Derived Property 8. Calculation of the Derived Property
Possible values of the derived property are: Possible values of the derived property are:
o PVALID o PVALID
o ID_PVAL o ID_PVAL
o FREE_PVAL o FREE_PVAL
o CONTEXTJ o CONTEXTJ
o CONTEXTO o CONTEXTO
o DISALLOWED o DISALLOWED
o ID_DIS o ID_DIS
o FREE_DIS o FREE_DIS
o UNASSIGNED o UNASSIGNED
Note: The value of the derived property calculated can depend on the Note: The value of the derived property calculated can depend on the
string class; for example, if an identifier used in an application string class; for example, if an identifier used in an application
protocol is defined as using or subclassing the PRECIS protocol is defined as profiling the PRECIS IdentifierClass then a
IdentifierClass then a space character such as U+0020 would be space character such as U+0020 would be assigned to ID_DIS, whereas
assigned to ID_DIS, whereas if an identifier is defined as using or if an identifier is defined as profiling the PRECIS FreeformClass
subclassing the PRECIS FreeformClass then the character would be then the character would be assigned to FREE_PVAL. For the sake of
assigned to FREE_PVAL. For the sake of brevity, the designation brevity, the designation "FREE_PVAL" is used in the code point
"FREE_PVAL" is used in the code point tables, instead of the longer tables, instead of the longer designation "ID_DIS or FREE_PVAL". In
designation "ID_DIS or FREE_PVAL". In practice, the derived practice, the derived properties ID_PVAL and FREE_DIS are not used in
properties ID_PVAL and FREE_DIS are not used in this specification, this specification, since every ID_PVAL code point is PVALID and
since every ID_PVAL code point is PVALID and every FREE_DIS code every FREE_DIS code point is DISALLOWED.
point is DISALLOWED.
The algorithm to calculate the value of the derived property is as The algorithm to calculate the value of the derived property is as
follows. (Note: Use of the name of a rule (such as "Exception") follows. (Note: Use of the name of a rule (such as "Exception")
implies the set of code points that the rule defines, whereas the implies the set of code points that the rule defines, whereas the
same name as a function call (such as "Exception(cp)") implies the same name as a function call (such as "Exception(cp)") implies the
value that the code point has in the Exceptions table.) value that the code point has in the Exceptions table.)
If .cp. .in. Exceptions Then Exceptions(cp); If .cp. .in. Exceptions Then Exceptions(cp);
Else If .cp. .in. BackwardCompatible Then BackwardCompatible(cp); Else If .cp. .in. BackwardCompatible Then BackwardCompatible(cp);
Else If .cp. .in. Unassigned Then UNASSIGNED; Else If .cp. .in. Unassigned Then UNASSIGNED;
skipping to change at page 23, line 25 skipping to change at page 22, line 24
Else If .cp. .in. PrecisIgnorableProperties Then DISALLOWED; Else If .cp. .in. PrecisIgnorableProperties Then DISALLOWED;
Else If .cp. .in. Controls Then DISALLOWED; Else If .cp. .in. Controls Then DISALLOWED;
Else If .cp. .in. HasCompat Then ID_DIS or FREE_PVAL; Else If .cp. .in. HasCompat Then ID_DIS or FREE_PVAL;
Else If .cp. .in. LetterDigits Then PVALID; Else If .cp. .in. LetterDigits Then PVALID;
Else If .cp. .in. OtherLetterDigits Then ID_DIS or FREE_PVAL; Else If .cp. .in. OtherLetterDigits Then ID_DIS or FREE_PVAL;
Else If .cp. .in. Spaces Then ID_DIS or FREE_PVAL; Else If .cp. .in. Spaces Then ID_DIS or FREE_PVAL;
Else If .cp. .in. Symbols Then ID_DIS or FREE_PVAL; Else If .cp. .in. Symbols Then ID_DIS or FREE_PVAL;
Else If .cp. .in. Punctuation Then ID_DIS or FREE_PVAL; Else If .cp. .in. Punctuation Then ID_DIS or FREE_PVAL;
Else DISALLOWED; Else DISALLOWED;
8. Code Points 9. IANA Considerations
The Categories and Rules defined under Section 6 and Section 7 apply 9.1. PRECIS Derived Property Value Registry
to all Unicode code points. The table in Appendix A shows, for
illustrative purposes, the consequences of the categories and
classification rules, and the resulting property values.
The list of code points that can be found in Appendix A is non- IANA is requested to create a PRECIS-specific registry with the
normative. Instead, the rules defined by Section 6 and Section 7 are Derived Properties for the versions of Unicode that are released
normative, and any tables are derived from the rules. after (and including) version 6.2. The derived property value is to
be calculated in cooperation with a designated expert [RFC5226]
according to the rules specified under Section 7 and Section 8, not
by copying the non-normative table found under Appendix A.
9. Security Considerations The IESG is to be notified if backward-incompatible changes to the
table of derived properties are discovered or if other problems arise
during the process of creating the table of derived property values
or during expert review. Changes to the rules defined under
Section 7 and Section 8 require IETF Review.
9.1. General Issues 9.2. PRECIS Base Classes Registry
IANA is requested to create a registry of PRECIS string classes. In
accordance with [RFC5226], the registration policy is "RFC Required".
The registration template is as follows:
Base Class: [the name of the PRECIS string class]
Description: [a brief description of the PRECIS string class and its
intended use, e.g., "A sequence of letters, numbers, and symbols
that is used to identify or address a network entity."]
Specification: [the RFC number]
The initial registrations are as follows:
Base Class: FreeformClass.
Description: A sequence of letters, numbers, symbols, spaces, and
other code points that is used for free-form strings.
Specification: RFC XXXX. [Note to RFC Editor: please change XXXX to
the number issued for this specification.]
Base Class: IdentifierClass.
Description: A sequence of letters, numbers, and symbols that is
used to identify or address a network entity.
Specification: RFC XXXX. [Note to RFC Editor: please change XXXX to
the number issued for this specification.]
9.3. PRECIS Profiles Registry
IANA is requested to create a registry of profiles that use the
PRECIS string classes. In accordance with [RFC5226], the
registration policy is "Expert Review". This policy was chosen in
order to ensure that "customers" of PRECIS receive appropriate
guidance regarding the sometimes complex and subtle
internationalization issues related to profiles of PRECIS string
classes.
The registration template is as follows:
Profile: [the name of the profile]
Applicability: [the specific protocol elements to which this profile
applies, e.g., "Localparts in XMPP addresses."]
Base Class: [which PRECIS string class is being profiled]
Replaces: [the Stringprep profile that this PRECIS profile replaces,
if any]
Width Mapping: [the behavioral rule for handling of width, e.g.,
"Map fullwidth and halfwidth characters to their decomposition
equivalents."]
Additional Mappings: [any additional mappings are required or
recommended, e.g., "Map non-ASCII space characters to ASCII
space."]
Case Mapping: [the behavioral rule for handling of case, e.g., "Map
uppercase and titlecase characters to lowercase."]
Normalization: [which Unicode normalization form is applied, e.g.,
"NFC"]
Directionality: [the behavioral rule for handling of right-to-left
code points, e.g., "The 'Bidi Rule' defined in RFC 5893 applies."]
Exclusions: [a brief description of the specific code points or
characters categories are excluded, e.g., "Eight legacy characters
in the ASCII range" or "Any character that has a compatibility
equivalent, i.e., the HasCompat category"]
Enforcement: [which entities enforce the rules, and when that
enforcement occurs during protocol operations]
Specification: [a pointer to relevant documentation, such as an RFC
or Internet-Draft]
In order to request a review, the registrant shall send a completed
template to the precis@ietf.org list or its designated successor.
Factors to focus on while reviewing profile registrations include the
following:
o Is the problem well-defined?
o Does the specification define what kinds of applications are
involved and the protocol elements to which this profile applies?
o Would an existing PRECIS string class or profile solve the
problem?
o Are the defined exclusions a reasonable solution to the problem
for the relevant applications?
o Is the profile clearly defined?
o Does the profile reduce the degree to which human users could be
surprised by application behavior (the "principle of least user
surprise")?
o Is the profile based on an appropriate dividing line between user
interface (culture, context, intent, locale, device limitations,
etc.) and the use of conformant strings in protocol elements?
o Are the normalization, case mapping, width mapping, additional
mapping, and directionality rules appropriate for the intended
use?
o Does the profile explain which entities enforce the rules of the
profile, and when such enforcement occurs during protocol
operations?
o Does the profile reduce the degree to which human users could be
surprised or confused by application behavior (the "principle of
least user surprise")?
o Does the profile introduce any new security concerns (e.g., false
positives for authentication or authorization)?
10. Security Considerations
10.1. General Issues
The security of applications that use this framework can depend in The security of applications that use this framework can depend in
part on the proper preparation and comparison of internationalized part on the proper preparation and comparison of internationalized
strings. For example, such strings can be used to make strings. For example, such strings can be used to make
authentication and authorization decisions, and the security of an authentication and authorization decisions, and the security of an
application could be compromised if an entity providing a given application could be compromised if an entity providing a given
string is connected to the wrong account or online resource based on string is connected to the wrong account or online resource based on
different interpretations of the string. different interpretations of the string.
Specifications of application protocols that use this framework are Specifications of application protocols that use this framework are
encouraged to describe how internationalized strings are used in the encouraged to describe how internationalized strings are used in the
protocol, including the security implications of any false positives protocol, including the security implications of any false positives
and false negatives that might result from various comparison and false negatives that might result from various comparison
operations. For some helpful guidelines, refer to [RFC6943], operations. For some helpful guidelines, refer to [RFC6943],
[RFC5890], [UTR36], and [UTR39]. [RFC5890], [UTR36], and [UTR39].
9.2. Use of the IdentifierClass 10.2. Use of the IdentifierClass
Strings that conform to the IdentifierClass and any subclass thereof Strings that conform to the IdentifierClass and any profile thereof
are intended to be relatively safe for use in a broad range of are intended to be relatively safe for use in a broad range of
applications, primarily because they include only letters, digits, applications, primarily because they include only letters, digits,
and "grandfathered" non-space characters from the ASCII range; thus and "grandfathered" non-space characters from the ASCII range; thus
they exclude spaces, characters with compatibility equivalents, and they exclude spaces, characters with compatibility equivalents, and
almost all symbols and punctuation marks. However, because such almost all symbols and punctuation marks. However, because such
strings can still include so-called confusable characters (see strings can still include so-called confusable characters (see
Section 9.5, protocol designers and implementers are encouraged to Section 10.5, protocol designers and implementers are encouraged to
pay close attention to the security considerations described pay close attention to the security considerations described
elsewhere in this document. elsewhere in this document.
9.3. Use of the FreeformClass 10.3. Use of the FreeformClass
Strings that conform to the FreeformClass and many subclasses thereof Strings that conform to the FreeformClass and many profiles thereof
can include virtually any Unicode character. This makes the can include virtually any Unicode character. This makes the
FreeformClass quite expressive, but also problematic from the FreeformClass quite expressive, but also problematic from the
perspective of possible user confusion. Protocol designers are perspective of possible user confusion. Protocol designers are
hereby warned that the FreeformClass contains codepoints they might hereby warned that the FreeformClass contains codepoints they might
not understand, and are encouraged to use or subclass the not understand, and are encouraged to profile the IdentifierClass
IdentifierClass wherever feasible; however, if an application wherever feasible; however, if an application protocol requires more
protocol requires more code points than are allowed by the code points than are allowed by the IdentifierClass, protocol
IdentifierClass, protocol designers are encouraged to define a designers are encouraged to define a profile of the FreeformClass
subclass of the FreeformClass that restricts the allowable code that restricts the allowable code points as tightly as possible.
points as tightly as possible. (The working group considered the (The working group considered the option of allowing superclasses as
option of allowing superclasses as well as subclasses of PRECIS well as profiles of PRECIS string classes, but decided against
string classes, but decided against allowing superclasses to reduce allowing superclasses to reduce the likelihood of security and
the likelihood of security and interoperability problems.) interoperability problems.)
9.4. Local Character Set Issues 10.4. Local Character Set Issues
When systems use local character sets other than ASCII and Unicode, When systems use local character sets other than ASCII and Unicode,
these specifications leave the problem of converting between the these specifications leave the problem of converting between the
local character set and Unicode up to the application or local local character set and Unicode up to the application or local
system. If different applications (or different versions of one system. If different applications (or different versions of one
application) implement different rules for conversions among coded application) implement different rules for conversions among coded
character sets, they could interpret the same name differently and character sets, they could interpret the same name differently and
contact different application servers or other network entities. contact different application servers or other network entities.
This problem is not solved by security protocols, such as Transport This problem is not solved by security protocols, such as Transport
Layer Security (TLS) [RFC5246] and the Simple Authentication and Layer Security (TLS) [RFC5246] and the Simple Authentication and
Security Layer (SASL) [RFC4422], that do not take local character Security Layer (SASL) [RFC4422], that do not take local character
sets into account. sets into account.
9.5. Visually Similar Characters 10.5. Visually Similar Characters
Some characters are visually similar and thus can cause confusion Some characters are visually similar and thus can cause confusion
among humans. Such characters are often called "confusable among humans. Such characters are often called "confusable
characters" or "confusables". characters" or "confusables".
The problem of confusable characters is not necessarily caused by the The problem of confusable characters is not necessarily caused by the
use of Unicode code points outside the ASCII range. For example, in use of Unicode code points outside the ASCII range. For example, in
some presentations and to some individuals the string "ju1iet" some presentations and to some individuals the string "ju1iet"
(spelled with the Arabic numeral one as the third character) might (spelled with the Arabic numeral one as the third character) might
appear to be the same as "juliet" (spelled with the lowercase version appear to be the same as "juliet" (spelled with the lowercase version
skipping to change at page 26, line 16 skipping to change at page 27, line 31
encouraged to define and implement consistent policies regarding the encouraged to define and implement consistent policies regarding the
registration, storage, and presentation of visually similar registration, storage, and presentation of visually similar
characters. The following recommendations are appropriate: characters. The following recommendations are appropriate:
1. An application service SHOULD define a policy that specifies the 1. An application service SHOULD define a policy that specifies the
scripts or blocks of characters that the service will allow to be scripts or blocks of characters that the service will allow to be
registered (e.g., in an account name) or stored (e.g., in a file registered (e.g., in an account name) or stored (e.g., in a file
name). Such a policy SHOULD be informed by the languages and name). Such a policy SHOULD be informed by the languages and
scripts that are used to write registered account names; in scripts that are used to write registered account names; in
particular, to reduce confusion, the service SHOULD forbid particular, to reduce confusion, the service SHOULD forbid
registration or storage of stings that contain characters from registration or storage of strings that contain characters from
more than one script and SHOULD restrict registrations to more than one script and SHOULD restrict registrations to
characters drawn from a very small number of scripts (e.g., characters drawn from a very small number of scripts (e.g.,
scripts that are well-understood by the administrators of the scripts that are well-understood by the administrators of the
service, to improve manageability). service, to improve manageability).
2. User-oriented application software SHOULD define a policy that 2. User-oriented application software SHOULD define a policy that
specifies how internationalized strings will be presented to a specifies how internationalized strings will be presented to a
human user. Because every human user of such software has a human user. Because every human user of such software has a
preferred language or a small set of preferred languages, the preferred language or a small set of preferred languages, the
software SHOULD gather that information either explicitly from software SHOULD gather that information either explicitly from
the user or implicitly via the operating system of the user's the user or implicitly via the operating system of the user's
skipping to change at page 26, line 39 skipping to change at page 28, line 5
because most scripts are typically contained in one or more because most scripts are typically contained in one or more
blocks of characters, the software SHOULD warn the user when blocks of characters, the software SHOULD warn the user when
presenting a string that mixes characters from more than one presenting a string that mixes characters from more than one
script or block, or that uses characters outside the normal range script or block, or that uses characters outside the normal range
of the user's preferred language(s). (Such a recommendation is of the user's preferred language(s). (Such a recommendation is
not intended to discourage communication across different not intended to discourage communication across different
communities of language users; instead, it recognizes the communities of language users; instead, it recognizes the
existence of such communities and encourages due caution when existence of such communities and encourages due caution when
presenting unfamiliar scripts or characters to human users.) presenting unfamiliar scripts or characters to human users.)
9.6. Security of Passwords The challenges inherent in supporting the full range of Unicode code
points have in the past led some to hope for a way to
programmatically negotiate more restrictive ranges based on locale,
script, or other relevant factors, to tag the locale associated with
a particular string, etc. As a general-purpose internationalization
technology, the PRECIS framework does not include such mechanisms.
10.6. Security of Passwords
Two goals of passwords are to maximize the amount of entropy and to Two goals of passwords are to maximize the amount of entropy and to
minimize the potential for false positives. These goals can be minimize the potential for false positives. These goals can be
achieved in part by allowing a wide range of code points and by achieved in part by allowing a wide range of code points and by
ensuring that passwords are handled in such a way that code points ensuring that passwords are handled in such a way that code points
are not compared aggressively. Therefore, it is NOT RECOMMENDED for are not compared aggressively. Therefore, it is NOT RECOMMENDED for
application protocols to subclass the FreeformClass for use in application protocols to profile the FreeformClass for use in
passwords in a way that removes entire categories (e.g., by passwords in a way that removes entire categories (e.g., by
disallowing symbols or punctuation). Furthermore, it is NOT disallowing symbols or punctuation). Furthermore, it is NOT
RECOMMENDED for application protocols to map uppercase and titlecase RECOMMENDED for application protocols to map uppercase and titlecase
code points to their lowercase equivalents in such strings; instead, code points to their lowercase equivalents in such strings; instead,
it is RECOMMENDED to preserve the case of all code points contained it is RECOMMENDED to preserve the case of all code points contained
in such strings and to compare them in a case-sensitive manner. in such strings and to compare them in a case-sensitive manner.
That said, software implementers need to be aware that there exist That said, software implementers need to be aware that there exist
tradeoffs between entropy and usability. For example, allowing a tradeoffs between entropy and usability. For example, allowing a
user to establish a password containing "uncommon" code points might user to establish a password containing "uncommon" code points might
skipping to change at page 27, line 23 skipping to change at page 28, line 44
reuse technologies that themselves process passwords (one example of reuse technologies that themselves process passwords (one example of
such a technology is the Simple Authentication and Security Layer such a technology is the Simple Authentication and Security Layer
[RFC4422]). Moreover, passwords are often carried by a sequence of [RFC4422]). Moreover, passwords are often carried by a sequence of
protocols with backend authentication systems or data storage systems protocols with backend authentication systems or data storage systems
such as RADIUS [RFC2865] and LDAP [RFC4510]. Developers of such as RADIUS [RFC2865] and LDAP [RFC4510]. Developers of
application protocols are encouraged to look into reusing these application protocols are encouraged to look into reusing these
profiles instead of defining new ones, so that end-user expectations profiles instead of defining new ones, so that end-user expectations
about passwords are consistent no matter which application protocol about passwords are consistent no matter which application protocol
is used. is used.
10. IANA Considerations
10.1. PRECIS Derived Property Value Registry
IANA is requested to create a PRECIS-specific registry with the
Derived Properties for the versions of Unicode that are released
after (and including) version 6.1. The derived property value is to
be calculated in cooperation with a designated expert [RFC5226]
according to the rules specified under Section 6 and Section 7, not
by copying the non-normative table found under Appendix A.
The IESG is to be notified if backward-incompatible changes to the
table of derived properties are discovered or if other problems arise
during the process of creating the table of derived property values
or during expert review. Changes to the rules defined under
Section 6 and Section 7) require IETF Review, as described in
[RFC5226].
10.2. PRECIS Base Classes Registry
IANA is requested to create a registry of PRECIS string classes. In
accordance with [RFC5226], the registration policy is "RFC Required".
The registration template is as follows:
Base Class: [the name of the PRECIS string class]
Description: [a brief description of the PRECIS string class and its
intended use, e.g., "A sequence of letters, numbers, and symbols
that is used to identify or address a network entity."]
Width Mapping: [the behavioral rule for handling of width, e.g.,
"Map fullwidth and halfwidth characters to their decomposition
equivalents."]
Additional Mappings: [any additional mappings are required or
recommended, e.g., "Map non-ASCII space characters to ASCII
space."; or "Application Specific" if to be defined by protocols
that use the PRECIS string class]
Case Mapping: [the behavioral rule for handling of case, e.g., "Map
uppercase and titlecase characters to lowercase."; or "Application
Specific" if to be defined by protocols that use the PRECIS string
class]
Normalization: [which Unicode normalization form is applied, e.g.,
"NFC"; or "Application Specific" if to be defined by protocols
that use the PRECIS string class]
Directionality: [the behavioral rule for handling of right-to-left
code points, e.g., "The 'Bidi Rule' defined in RFC 5893 applies.";
or "Application Specific" if to be defined by protocols that use
the PRECIS string class]
Specification: [the RFC number]
The initial registrations are as follows:
Base Class: FreeformClass.
Description: A sequence of letters, numbers, symbols, spaces, and
other code points that is used for free-form strings.
Width Mapping: Application Specific.
Additional Mappings: Application Specific.
Case Mapping: Application Specific.
Normalization: Application Specific.
Directionality: Application Specific.
Specification: RFC XXXX. [Note to RFC Editor: please change XXXX to
the number issued for this specification.]
Base Class: IdentifierClass.
Description: A sequence of letters, numbers, and symbols that is
used to identify or address a network entity.
Width Mapping: Application Specific.
Additional Mappings: Application Specific.
Case Mapping: Application Specific.
Normalization: Application Specific.
Directionality: Application Specific.
Specification: RFC XXXX. [Note to RFC Editor: please change XXXX to
the number issued for this specification.]
10.3. PRECIS Subclasses Registry
IANA is requested to create a registry of subclasses that use the
PRECIS string classes. In accordance with [RFC5226], the
registration policy is "Expert Review". This policy was chosen in
order to ensure that "customers" of PRECIS receive appropriate
guidance regarding the sometimes complex and subtle
internationalization issues related to subclassing of PRECIS string
classes.
The registration template is as follows:
Subclass: [the name of the subclass]
Base Class: [which PRECIS string class is being subclassed]
Exclusions: [a brief description of the specific code points that
are excluded or of the properties based on which characters are
excluded, e.g., "Eight legacy characters in the ASCII range" or
"Any character that has a compatibility equivalent, i.e., the
HasCompat category"]
Specification: [a pointer to relevant documentation, such as an RFC
or Internet-Draft]
In order to request a review, the registrant shall send a completed
template to the precis@ietf.org list or its designated successor.
Factors to focus on while reviewing subclass registrations include
the following:
o Is the problem well-defined?
o Is it clear what applications will use this subclass?
o Would an existing PRECIS string class or subclass solve the
problem?
o Are the defined exclusions a reasonable solution to the problem
for the relevant applications?
o Is the subclass clearly defined?
o Does the subclass reduce the degree to which human users could be
surprised by application behavior (the "principle of least user
surprise")?
o Is the subclass based on an appropriate dividing line between user
interface (culture, context, intent, locale, device limitations,
etc.) and the use of conformant strings in protocol elements?
o Does the subclass introduce any new security concerns (e.g., false
positives for authentication or authorization)?
10.4. PRECIS Usage Registry
IANA is requested to create a registry of application protocols that
use the PRECIS string classes. The registry will include one entry
for each use (e.g., if a protocol uses both the IdentifierClass and
the FreeformClass then the specification for that protocol would
submit two registrations). In accordance with [RFC5226], the
registration policy is "Expert Review". This policy was chosen in
order to ensure that "customers" of PRECIS receive appropriate
guidance regarding the sometimes complex and subtle
internationalization issues related to use of PRECIS string classes.
The registration template is as follows:
Applicability: [the specific protocol elements to which this usage
applies, e.g., "Localparts in XMPP addresses."]
Base Class: [the PRECIS string class that is being used or
subclassed]
Subclass: [whether the protocol has defined a subclass of the PRECIS
string class and, if so, the name of the subclass, e.g., "Yes,
LocalpartIdentifierClass."]
Replaces: [the Stringprep profile that this PRECIS usage replaces,
if any]
Width Mapping: [the behavioral rule for handling of width, e.g.,
"Map fullwidth and halfwidth characters to their decomposition
equivalents."]
Additional Mappings: [any additional mappings are required or
recommended, e.g., "Map non-ASCII space characters to ASCII
space."]
Case Mapping: [the behavioral rule for handling of case, e.g., "Map
uppercase and titlecase characters to lowercase."]
Normalization: [which Unicode normalization form is applied, e.g.,
"NFC"]
Directionality: [the behavioral rule for handling of right-to-left
code points, e.g., "The 'Bidi Rule' defined in RFC 5893 applies."]
Specification: [a pointer to relevant documentation, such as an RFC
or Internet-Draft]
In order to request a review, the registrant shall send a completed
template to the precis@ietf.org list or its designated successor.
Factors to focus on while reviewing usage registrations include the
following:
o Does the specification define what kinds of applications are
involved and the protocol elements to which this usage applies?
o Is there a PRECIS string class or subclass that would be more
appropriate to use?
o Are the normalization, case mapping, width mapping, additional
mapping, and directionality rules appropriate for the intended
use?
o Does the usage reduce the degree to which human users could be
surprised by application behavior (the "principle of least user
surprise")?
o Is the usage based on an appropriate dividing line between user
interface (culture, context, intent, locale, device limitations,
etc.) and the use of conformant strings in protocol elements?
o Does the usage introduce any new security concerns (e.g., false
positives for authentication or authorization)?
11. Interoperability Considerations 11. Interoperability Considerations
Although strings that are consumed in PRECIS-based application Although strings that are consumed in PRECIS-based application
protocols are often encoded using UTF-8 [RFC3629], the exact encoding protocols are often encoded using UTF-8 [RFC3629], the exact encoding
is a matter for the application protocol that reuses PRECIS, not for is a matter for the application protocol that uses PRECIS, not for
the PRECIS framework. the PRECIS framework.
It is known that some existing systems are unable to support the full It is known that some existing systems are unable to support the full
Unicode character set, or even any characters outside the ASCII Unicode character set, or even any characters outside the ASCII
range. If two (or more) applications need to interoperate when range. If two (or more) applications need to interoperate when
exchanging data (e.g., for the purpose of authenticating a username exchanging data (e.g., for the purpose of authenticating a username
or password), they will naturally need have in common at least one or password), they will naturally need have in common at least one
coded character set (as defined by [RFC6365]). Establishing such a coded character set (as defined by [RFC6365]). Establishing such a
baseline is a matter for the application protocol that reuses PRECIS, baseline is a matter for the application protocol that uses PRECIS,
not for the PRECIS framework. not for the PRECIS framework.
The PRECIS framework, which is defined in terms of the latest version
of Unicode as of the time of this writing (6.2), treats the character
U+19DA NEW TAI LUE THAM as DISALLOWED. Implementers need to be aware
that this treatment is different from IDNA2008 (originally defined in
terms of Unicode 5.2), which treats U+19DA as PVALID.
12. References 12. References
12.1. Normative References 12.1. Normative References
[I-D.ietf-precis-mappings] [I-D.ietf-precis-mappings]
Yoneya, Y. and T. NEMOTO, "Mapping characters for precis Yoneya, Y. and T. NEMOTO, "Mapping characters for precis
classes", draft-ietf-precis-mappings-02 (work in classes", draft-ietf-precis-mappings-03 (work in
progress), May 2013. progress), August 2013.
[RFC20] Cerf, V., "ASCII format for network interchange", RFC 20, [RFC20] Cerf, V., "ASCII format for network interchange", RFC 20,
October 1969. October 1969.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC5198] Klensin, J. and M. Padlipsky, "Unicode Format for Network [RFC5198] Klensin, J. and M. Padlipsky, "Unicode Format for Network
Interchange", RFC 5198, March 2008. Interchange", RFC 5198, March 2008.
skipping to change at page 34, line 27 skipping to change at page 32, line 14
<http://unicode.org/reports/tr39/>. <http://unicode.org/reports/tr39/>.
URIs URIs
[1] <http://unicode.org/Public/UNIDATA/PropertyAliases.txt> [1] <http://unicode.org/Public/UNIDATA/PropertyAliases.txt>
[2] <http://unicode.org/Public/UNIDATA/DerivedCoreProperties.txt> [2] <http://unicode.org/Public/UNIDATA/DerivedCoreProperties.txt>
Appendix A. Codepoint Table Appendix A. Codepoint Table
WARNING: The following table is provisional and is still being If one applies the property calculation rules from Section 8 to the
verified!
If one applies the property calculation rules from Section 7 to the
code points 0x0000 to 0x10FFFF in Unicode 6.2, the result is as shown code points 0x0000 to 0x10FFFF in Unicode 6.2, the result is as shown
in the following table, in Unicode Character Database (UCD) format. in the following table, in Unicode Character Database (UCD) format.
The columns of the table are as follows: The columns of the table are as follows:
1. The code point or codepoint range. 1. The code point or codepoint range.
2. The assignment for the code point or range, where the value is 2. The assignment for the code point or range, where the value is
one of PVALID, DISALLOWED, UNASSIGNED, CONTEXTO, CONTEXTJ, or one of PVALID, DISALLOWED, UNASSIGNED, CONTEXTO, CONTEXTJ, or
FREE_PVAL (which includes ID_DIS). FREE_PVAL (which includes ID_DIS).
3. The name or names for the code point or range. 3. The name or names for the code point or range.
skipping to change at page 36, line 9 skipping to change at page 33, line 41
0386 ; PVALID # GR CAP LET ALPHA W TONOS 0386 ; PVALID # GR CAP LET ALPHA W TONOS
0387 ; FREE_PVAL # GREEK ANO TELEIA 0387 ; FREE_PVAL # GREEK ANO TELEIA
0388..038A ; PVALID # GR CAP LET EPSILON W TONOS..GR CAP 0388..038A ; PVALID # GR CAP LET EPSILON W TONOS..GR CAP
038B ; UNASSIGNED # <reserved> 038B ; UNASSIGNED # <reserved>
038C ; PVALID # GREEK CAP LET OMICRON W TONOS 038C ; PVALID # GREEK CAP LET OMICRON W TONOS
038D ; UNASSIGNED # <reserved> 038D ; UNASSIGNED # <reserved>
038E..03A1 ; PVALID # GR CAP LET EPSILON W TONOS..GR CAP 038E..03A1 ; PVALID # GR CAP LET EPSILON W TONOS..GR CAP
03A2 ; UNASSIGNED # <reserved> 03A2 ; UNASSIGNED # <reserved>
03A3..03CF ; PVALID # GREEK CAP LET SIGMA..GR CAP 03A3..03CF ; PVALID # GREEK CAP LET SIGMA..GR CAP
03D0..03D2 ; FREE_PVAL # GR BETA SYM..GR UPSILON W HOOK 03D0..03D2 ; FREE_PVAL # GR BETA SYM..GR UPSILON W HOOK
03D3..03D4 ; PVALID # GR UPSILON W ACUTE AND HOOK..GR UP 03D3..03D4 ; FREE_PVAL # GR UPSILON W ACUTE AND HOOK..GR UP
03D5..03D6 ; FREE_PVAL # GR PHI SYM..GR PI SYM 03D5..03D6 ; FREE_PVAL # GR PHI SYM..GR PI SYM
03D7..03EF ; PVALID # GR KAI SYM..COPT SM LET DEI 03D7..03EF ; PVALID # GR KAI SYM..COPT SM LET DEI
03F0..03F2 ; FREE_PVAL # GR KAPPA SYM..GR LUNATE SIGMA 03F0..03F2 ; FREE_PVAL # GR KAPPA SYM..GR LUNATE SIGMA
03F3 ; PVALID # GREEK LET YOT 03F3 ; PVALID # GREEK LET YOT
03F4..03F6 ; FREE_PVAL # GR CAP THETA..GR REV LUNATE EPSILON 03F4..03F6 ; FREE_PVAL # GR CAP THETA..GR REV LUNATE EPSILON
03F7..03F8 ; PVALID # GR CAP LET SHO..GR SM LET SHO 03F7..03F8 ; PVALID # GR CAP LET SHO..GR SM LET SHO
03F9 ; FREE_PVAL # GREEK CAP LUNATE SIGMA SYM 03F9 ; FREE_PVAL # GREEK CAP LUNATE SIGMA SYM
03FA..0481 ; PVALID # GR CAP LET SAN..CYR SML LET KOPPA 03FA..0481 ; PVALID # GR CAP LET SAN..CYR SML LET KOPPA
0482 ; FREE_PVAL # CYR THOUSANDS SIGN 0482 ; FREE_PVAL # CYR THOUSANDS SIGN
0483..0487 ; PVALID # COMB CYR TITLO..COMB CYR POK 0483..0487 ; PVALID # COMB CYR TITLO..COMB CYR POK
skipping to change at page 47, line 40 skipping to change at page 45, line 24
1944..1945 ; FREE_PVAL # LIMBU EXCLAM MARK..LIMBU QUEST MARK 1944..1945 ; FREE_PVAL # LIMBU EXCLAM MARK..LIMBU QUEST MARK
1946..196D ; PVALID # LIMBU DIG ZERO..TAI LE LET AI 1946..196D ; PVALID # LIMBU DIG ZERO..TAI LE LET AI
196E..196F ; UNASSIGNED # <reserved>..<reserved> 196E..196F ; UNASSIGNED # <reserved>..<reserved>
1970..1974 ; PVALID # TAI LE LET TONE-2..TAI LE LET TONE- 1970..1974 ; PVALID # TAI LE LET TONE-2..TAI LE LET TONE-
1975..197F ; UNASSIGNED # <reserved>..<reserved> 1975..197F ; UNASSIGNED # <reserved>..<reserved>
1980..19AB ; PVALID # NEW TAI LUE LET HIGH QA..NEW TAI LU 1980..19AB ; PVALID # NEW TAI LUE LET HIGH QA..NEW TAI LU
19AC..19AF ; UNASSIGNED # <reserved>..<reserved> 19AC..19AF ; UNASSIGNED # <reserved>..<reserved>
19B0..19C9 ; PVALID # NEW TAI LUE VOW SIGN VOW SHORT..NEW 19B0..19C9 ; PVALID # NEW TAI LUE VOW SIGN VOW SHORT..NEW
19CA..19CF ; UNASSIGNED # <reserved>..<reserved> 19CA..19CF ; UNASSIGNED # <reserved>..<reserved>
19D0..19D9 ; PVALID # NEW TAI LUE DIG ZERO..NEW TAI DIG N 19D0..19D9 ; PVALID # NEW TAI LUE DIG ZERO..NEW TAI DIG N
19DA ; FREE_PVAL # NEW TAI LUE THAM 19DA ; DISALLOWED # NEW TAI LUE THAM
19DB..19DD ; UNASSIGNED # <reserved>..<reserved> 19DB..19DD ; UNASSIGNED # <reserved>..<reserved>
19DE..19FF ; FREE_PVAL # NEW TAI LUE SIGN LAE..KHMER SYM DAP 19DE..19FF ; FREE_PVAL # NEW TAI LUE SIGN LAE..KHMER SYM DAP
1A00..1A1B ; PVALID # BUGIN LET KA..BUGIN VOW SIGN AE 1A00..1A1B ; PVALID # BUGIN LET KA..BUGIN VOW SIGN AE
1A1C..1A1D ; UNASSIGNED # <reserved>..<reserved> 1A1C..1A1D ; UNASSIGNED # <reserved>..<reserved>
1A1E..1A1F ; FREE_PVAL # BUGIN PALLAWA..BUGIN END OF SECTION 1A1E..1A1F ; FREE_PVAL # BUGIN PALLAWA..BUGIN END OF SECTION
1A20..1A5E ; PVALID # TAI THAM LET HIGH KA..TAI THAM CONS 1A20..1A5E ; PVALID # TAI THAM LET HIGH KA..TAI THAM CONS
1A5F ; UNASSIGNED # <reserved> 1A5F ; UNASSIGNED # <reserved>
1A60..1A7C ; PVALID # TAI THAM SIGN SAKOT..TAI THAM SIGN 1A60..1A7C ; PVALID # TAI THAM SIGN SAKOT..TAI THAM SIGN
1A7D..1A7E ; UNASSIGNED # <reserved>..<reserved> 1A7D..1A7E ; UNASSIGNED # <reserved>..<reserved>
1A7F..1A89 ; PVALID # TAI THAM COMB CRYPT DOT..TAI THAM D 1A7F..1A89 ; PVALID # TAI THAM COMB CRYPT DOT..TAI THAM D
skipping to change at page 48, line 49 skipping to change at page 46, line 33
1D3C..1D4D ; FREE_PVAL # MOD LET CAP O..MOD LET S 1D3C..1D4D ; FREE_PVAL # MOD LET CAP O..MOD LET S
1D4E ; PVALID # MOD LET SM TURNED I 1D4E ; PVALID # MOD LET SM TURNED I
1D4F..1D6A ; FREE_PVAL # MOD LET SM K..GREEK SUB SMA 1D4F..1D6A ; FREE_PVAL # MOD LET SM K..GREEK SUB SMA
1D6B..1D77 ; PVALID # LAT SM LET UE..LAT SM LET TU 1D6B..1D77 ; PVALID # LAT SM LET UE..LAT SM LET TU
1D78 ; FREE_PVAL # MOD LET CYR EN 1D78 ; FREE_PVAL # MOD LET CYR EN
1D79..1D9A ; PVALID # LAT SM LET INSULAR G..LAT SM LE 1D79..1D9A ; PVALID # LAT SM LET INSULAR G..LAT SM LE
1D9B..1DBF ; FREE_PVAL # MOD LET SM TURNED ALPHA..MOD 1D9B..1DBF ; FREE_PVAL # MOD LET SM TURNED ALPHA..MOD
1DC0..1DE6 ; PVALID # COMB DOTTED GRAVE ACCENT..COMB LAT 1DC0..1DE6 ; PVALID # COMB DOTTED GRAVE ACCENT..COMB LAT
1DE7..1DFB ; UNASSIGNED # <reserved>..<reserved> 1DE7..1DFB ; UNASSIGNED # <reserved>..<reserved>
1DFC..1DFF ; PVALID # COMB DOUBLE INV BREVE BEL..COMB R 1DFC..1DFF ; PVALID # COMB DOUBLE INV BREVE BEL..COMB R
1E9A ; FREE_PVAL # LAT SM LET A WITH R HALF RING 1E9A..1E9B ; FREE_PVAL # LAT SM LET A WITH R HALF RING..LAT
1E9B..1F15 ; PVALID # LAT SM LET LONG S W DOT ABOVE..GR 1E9C..1F15 ; PVALID # LAT SM LET LONG S W DIAG STR..GR
1F16..1F17 ; UNASSIGNED # <reserved>..<reserved> 1F16..1F17 ; UNASSIGNED # <reserved>..<reserved>
1F18..1F1D ; FREE_PVAL # GREEK CAP LET EPSILON W PSILI..GRE 1F18..1F1D ; FREE_PVAL # GREEK CAP LET EPSILON W PSILI..GRE
1F1E..1F1F ; UNASSIGNED # <reserved>..<reserved> 1F1E..1F1F ; UNASSIGNED # <reserved>..<reserved>
1F20..1F45 ; PVALID # GREEK SM LET ETA W PSILI..GREEK SMA 1F20..1F45 ; PVALID # GREEK SM LET ETA W PSILI..GREEK SMA
1F46..1F47 ; UNASSIGNED # <reserved>..<reserved> 1F46..1F47 ; UNASSIGNED # <reserved>..<reserved>
1F48..1F4D ; FREE_PVAL # GREEK CAP LET OMICRON W PSILI..GRE 1F48..1F4D ; FREE_PVAL # GREEK CAP LET OMICRON W PSILI..GRE
1F4E..1F4F ; UNASSIGNED # <reserved>..<reserved> 1F4E..1F4F ; UNASSIGNED # <reserved>..<reserved>
1F50..1F57 ; PVALID # GREEK SM LET UPSILON W PSILI..GREEK 1F50..1F57 ; PVALID # GREEK SM LET UPSILON W PSILI..GREEK
1F58 ; UNASSIGNED # <reserved> 1F58 ; UNASSIGNED # <reserved>
1F59 ; PVALID # GREEK CAP LET UPSILON W DASIA 1F59 ; PVALID # GREEK CAP LET UPSILON W DASIA
skipping to change at page 55, line 39 skipping to change at page 53, line 23
FB43..FB44 ; FREE_PVAL # HEBR LET FIN PE W DAGESH..HEBR L FB43..FB44 ; FREE_PVAL # HEBR LET FIN PE W DAGESH..HEBR L
FB45 ; UNASSIGNED # <reserved> FB45 ; UNASSIGNED # <reserved>
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FB4F..FBC1 ; FREE_PVAL # HEBR LIG ALEF LAMED..ARAB SYM S FB4F..FBC1 ; FREE_PVAL # HEBR LIG ALEF LAMED..ARAB SYM S
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FE20..FE26 ; PVALID # COMB LIG LEFT HALF..COMB CONJ MACRO FE20..FE26 ; PVALID # COMB LIG LEFT HALF..COMB CONJ MACRO
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E01F0..EFFFD; UNASSIGNED # <reserved>..<reserved> E01F0..EFFFD; UNASSIGNED # <reserved>..<reserved>
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Appendix B. Acknowledgements Appendix B. Acknowledgements
The authors would like to acknowledge the comments and contributions The authors would like to acknowledge the comments and contributions
of the following individuals: David Black, Mark Davis, Alan DeKok, of the following individuals: David Black, Mark Davis, Alan DeKok,
Martin Duerst, Patrik Faltstrom, Ted Hardie, Joe Hildebrand, Paul Martin Duerst, Patrik Faltstrom, Ted Hardie, Joe Hildebrand, Paul
Hoffman, Jeffrey Hutzelman, Simon Josefsson, John Klensin, Alexey Hoffman, Jeffrey Hutzelman, Simon Josefsson, John Klensin, Alexey
Melnikov, Takahiro Nemoto, Yoav Nir, Mike Parker, Pete Resnick, Melnikov, Takahiro Nemoto, Yoav Nir, Mike Parker, Pete Resnick,
Andrew Sullivan, Dave Thaler, and Yoshiro Yoneya. Andrew Sullivan, Dave Thaler, Yoshiro Yoneya, and Florian Zeitz.
Some algorithms and textual descriptions have been borrowed from Some algorithms and textual descriptions have been borrowed from
[RFC5892]. Some text regarding security has been borrowed from [RFC5892]. Some text regarding security has been borrowed from
[RFC5890] and [I-D.ietf-xmpp-6122bis]. [RFC5890] and [I-D.ietf-xmpp-6122bis].
Authors' Addresses Authors' Addresses
Peter Saint-Andre Peter Saint-Andre
Cisco Systems, Inc. Cisco Systems, Inc.
1899 Wynkoop Street, Suite 600 1899 Wynkoop Street, Suite 600
Denver, CO 80202 Denver, CO 80202
USA USA
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