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:

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:



Please fill all the sections A, B and C below.

(Please read Principles and Procedures Document for guidelines and details before filling this form.)
See http://www.dkuug.dk/JTC1/SC2/WG2/docs/summaryform.html for latest Form.
See http://www.dkuug.dk/JTC1/SC2/WG2/docs/principles.html for latest Principles and Procedures document.
See http://www.dkuug.dk/JTC1/SC2/WG2/docs/roadmaps.html for latest roadmaps.

(Form number: N2352-F (Original 1994-10-14; Revised 1995-01, 1995-04, 1996-04, 1996-08, 1999-03, 2001-05, 2001-09)

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?
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
4. The context of use for the proposed characters (type of use;
   common or rare)                                             common
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)
    If YES, reference: