These combining characters are named variation selector-17 (for U+E0100) through to variation selector-256 (U+E01EF), abbreviated VS17 – VS256.
Ideographic Variation Sequences
As of 12 December 2017[update], VS17 (U+E0100) to VS48 (U+E011F) are used in ideographic variation sequences in the Unicode Ideographic Variation Database (IVD).[3][4] These selectors are known as Ideographic Variation Selectors (IVS). They are not listed in the list of standardized variation sequence, instead they are listed in another Ideographic Variation Database.[3]
IVD collections
The following IVS collections are currently registered in the IVD:[3]
CID-keyed Japanese OpenType fonts. Defines at least one sequence for every Japanese kanji from the Adobe-Japan1 collection present in Unicode, even for those with only one glyph, both as future-proofing and to allow that (Japan-region) glyph to be uniquely referenced.[5]
Unicode characters corresponding to more than one glyph collected by the Han'yō Denshi programme, a union of the character repertoires of the legacy kanji character sets used by multiple administrative systems in Japan (precursor to Moji Jōhō Kiban).[6] Approximately 60% of the initial registration matches Adobe-Japan1 glyphs, but the existing Adobe-Japan1 variation sequences are not used for them.[7]
Unicode characters corresponding to more than one entry in the Moji Jōhō Kiban, a database of kanji used for administrative purposes in Japan. Supersedes and deprecates the Hanyo-Denshi collection, from which it retains 9866 of the existing IVSes.[6]
Similarly to the Moji Jōhō Kiban's role in Japan, the character repertoire of CNS 11643 (including draft revisions) is used for administrative purposes in Taiwan.[8] In some cases, multiple of these correspond to a single Unicode character.[9] Many of these cases are currently handled with mappings to the Supplementary Private Use Area.[9] However, the Taipei Computer Association, which represents the interests of Taiwan in the Ideographic Research Group, has been evaluating the feasibility of registering an additional IVD collection in the future.[9][10]
Aliprand, Joan; Winkler, Arnold (1998-02-24), "2.D.4 Variant Tag Mechanism", Preliminary Minutes - UTC #74 & L2 #171, Mountain View, CA - December 5, 1997
L2/98-277
Hiura, Hideki; Kobayashi, Tatsuo (1998-07-29), Plane 14 Variant tag
^Lunde, Ken; Muller, Eric (2017). "PRI 108: Combined registration of the Adobe-Japan1 collection and of sequences in that collection". Adobe/Unicode Consortium. Note that all Adobe-Japan1-6 kanji, except those twenty seven pointed out above, are given IVS assignments, including those that have only one form assigned. This is to ensure that each Adobe-Japan1-6 kanji can be uniquely and explicitly identified without referencing their default (IVS-less) encoding, and because kanji may be added in future Adobe-Japan1 Supplements that may be variants of such kanji.