L2/03-293
Proposal to add Private
Use Variation Selectors
Eric Muller, Adobe
Systems Inc.
August 23, 2003
The Unicode standard states in Section 15.6, Variation Selectors,
that:
Only the variation sequences specifically
defined in the file Standardized-Variants.txt in the Unicode Character
Database are sanctioned for standard use; in all other cases the
variation selector cannot change the visual appearance of the preceding
base character from what it would have had in the absence of the
variation selector.
It is anticipated that Variation Selectors will be used in
conjunction with CJK ideographs, e.g. to identify glyph variants.
However, the precise way in which VS will be used in this context
requires much research and experimentation. The clause above makes it
difficult to conduct such experiments in the context of large systems,
where some component may reject or otherwise prevent the use of
variation sequences not defined in the UCD. To enable such
experimentation, it would be useful to have Private Use Variation
Selectors that are not be subject to the clause above. The interchange
of a variation sequence involving a Private Use Variation Selector
would be allowed, and it could, in some implementations, modify the
visual appearance of the base character. The precise effect of the
variation sequence would be determined by a private agreement, much
like the meaning of a Private Use character is determined by private
agreement.
We propose to encode 256 Private Use Variation Selectors, as follow:
- PRIVATE
USE VARIATION SELECTOR-1 through PRIVATE USE VARIATION SELECTOR-16, at
code points U+FE10 through U+FE1F
- PRIVATE
USE VARIATION
SELECTOR-17 through PRIVATE USE VARIATION SELECTOR-256, at code points
U+E0200 through U+E02EF
The motivation is to have a large enough number of selectors
available, and to have some in the BMP so that experiments can be
performed in implementations that support only the BMP. The proposed
code points have been chosen to be adjacent to the existing Variation
Selector characters. In fact, the blocks Variation Selectors and
Variation Selectors Supplement could simply be extended.
The properties for those characters
would be the same as for the existing Variation Selector chracters:
- general category Mn
- canonical combining class
0
- bidirectional category
NSM
- no decomposition mapping
- no numeric value
- not mirrored
- no case mapping
A. Administrative
1. Title: Proposal to add Private Use Variation Selectors
2. Requester's name: Adobe Systems Inc. (contact: Eric Muller)
3. Requester type (Member body/Liaison/Individual contribution): expert contribution
4. Submission date: August 23, 2003
5. Requester's reference (if applicable):
6. (Choose one of the following:)
This is a complete proposal: Yes
or, More information will be provided later:
B. Technical - General
1. (Choose one of the following:)
a. This proposal is for a new script (set of characters): No
Proposed name of script:
b. The proposal is for addition of character(s) to an existing block: Yes
Name of the existing block: Variation Selectors and Variation Selectors Supplement
2. Number of characters in proposal: 256
3. Proposed category (see section II, Character Categories): A
4. Proposed Level of Implementation (1, 2 or 3) 1
(see clause 14, ISO/IEC 10646-1: 2000):
Is a rationale provided for the choice? No
If Yes, reference:
5. Is a repertoire including character names provided? Yes
a. If YES, are the names in accordance with the
'character naming guidelines in Annex L of ISO/IEC 10646-1: 2000? Yes
b. Are the character shapes attached in a legible form suitable for review?
No
6. Who will provide the appropriate computerized font (ordered preference:
True Type, or PostScript format) for publishing the standard?
Adobe Systems Inc, True Type
If available now, identify source(s) for the font (include address,
e-mail, ftp-site, etc.) and indicate the tools used:
Fontlab, by modification of the font for existing VS characters
7. References:
a. Are references (to other character sets, dictionaries, descriptive
texts etc.) provided? No
b. Are published examples of use (such as samples from newspapers,
magazines, or other sources) of proposed characters attached? No
8. Special encoding issues:
Does the proposal address other aspects of character data processing
(if applicable) such as input, presentation, sorting, searching, indexing,
transliteration etc. (if yes please enclose information)? No
_________________________________________________________________________
9. Additional
Information:
Submitters are invited to provide any additional information about
Properties of the proposed Character(s) or Script that will assist in
correct
understanding of and correct linguistic processing of the proposed
character(s)
or script. Examples of such properties are: Casing information, Numeric
information, Currency information, Display behaviour
information such as line breaks, widths etc., Combining behaviour,
Spacing behaviour, Directional behaviour,
Default Collation behaviour, relevance in
Mark Up
contexts, Compatibility equivalence and other Unicode normalization
related
information. See the Unicode standard at http://www.unicode.org/
for such information on other scripts. Also see Unicode Character
Database http://www.unicode.org/Public/UNIDATA/UnicodeCharacterDatabase.html
and associated Unicode Technical Reports for information needed for
consideration
by the Unicode Technical Committee for inclusion in the Unicode
Standard.
C. Technical -
Justification
1. Has this proposal for addition of character(s) been submitted before? No
If YES explain
2. Has contact been made to members of the user community (for example:
National Body, user groups of the script or characters,
other experts, etc.)? Yes
If YES, with whom? UTC
If YES, available relevant documents: L2/03-293
3. Information on the user community for the proposed characters
(for example: size, demographics, information technology use, or
publishing use) is included? No
Reference:
4. The context of use for the proposed characters (type of use;
common or rare) common
Reference:
5. Are the proposed characters in current use by the user community? No
If YES, where? Reference: available in fonts
6. After giving due considerations to the principles in Principles and
Procedures document (a WG 2 standing document) must the proposed
characters be entirely in the BMP? Yes for the first 16.
If YES, is a rationale provided? Yes
If YES, reference: see above
7. Should the proposed characters be kept together in a contiguous range
(rather than being scattered)? No
8. Can any of the proposed characters be considered a presentation form of an
existing character or character sequence? No
If YES, is a rationale for its inclusion provided?
If YES, reference:
9. Can any of the proposed characters be encoded using a composed character
sequence of either existing characters or other proposed characters? No
If YES, is a rationale for its inclusion provided?
If YES, reference:
10. Can any of the proposed character(s) be considered to be similar (in
appearance or function) to an existing character? No
If YES, is a rationale for its inclusion provided?
If YES, reference:
11. Does the proposal include use of combining characters and/or use of
composite sequences (see clauses 4.12 and 4.14
in ISO/IEC 10646-1: 2000)? No
If YES, is a rationale for such use provided?
If YES, reference:
Is a list of composite sequences and their corresponding glyph images
(graphic symbols) provided?
If YES, reference:
12. Does the proposal contain characters with any special properties such as
control function or similar semantics? Yes
If YES, describe in detail (include attachment if necessary) see above
13. Does the proposal contain any Ideographic compatibility character(s)? No
If YES, is the equivalent corresponding unified ideographic character(s)
identified?
If YES, reference: