Big 5 character set + additional HKSCS characters (partial - full = approx. 400 - 4818 characters) = approx. 14000 - 19000 characters
Function:: Replaces default forms with variants adjusted for vertical writing when in vertical writing mode. While most CJKV glyphs remain vertical when set in vertical writing mode, some take a different form (usually rotated and repositioned) for this purpose. Glyphs covered by this feature correspond to the set normally rotated in low-end DTP applications. In vertical writing mode, the opening parenthesis (U+FF08) is replaced by the rotated form (U+FE35).
Function:: To minimize the number of glyph alternates, it is sometimes desired to decompose a character into two glyphs. Additionally, it may be preferable to compose two characters into a single glyph for better glyph processing. This feature permits such composition/decompostion. The feature should be processed as the first feature processed, and should be processed only when it is called. In Syriac, the character 0x0732 is a combining mark that has a dot above AND a dot below the base character. To avoid multiple glyph variants to fit all base glyphs, the character is decomposed into two glyphs...a dot above and a dot below. These two glyphs can then be correctly placed using GPOS. In Arabic it might be preferred to combine the shadda with fatha (0x0651, 0x064E) into a ligature before processing shapes. This allows the font vendor to do special handling of the mark combination when doing further processing without requiring larger contextual rules.