Variation Selectors is a Unicode block containing 16 variation selectors used to specify a glyph variant for a preceding character. They are currently used to specify standardized variation sequences for mathematical symbols, emoji symbols, 'Phags-pa letters, and CJK unified ideographs corresponding to CJK compatibility ideographs. At present only standardized variation sequences with VS1–VS4, VS7, VS15 and VS16 have been defined; VS15 and VS16 are reserved to request that a character should be displayed as text or as an emoji respectively.[3][4]
These combining characters are named variation selector-1 (for U+FE00) through to variation selector-16 (U+FE0F), and are abbreviated VS1 – VS16. Each applies to the immediately preceding character.
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