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ljmo.yml
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ljmo.yml
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title: Leading Jamo Forms
registered: Microsoft
group: Topographical
state: required
script:
hang: 1
description: |
The Korean Hangul script is encoded in Unicode in two ways: first, as a series
of precomposed syllable graphemes (encoded from U+AC00 to U+D7AF); second, as
a series of indivdual, conjoining *jamo*. Korean syllables form a LVT?
(leading consonant, vowel, optional trailing consonant) pattern; the leading consonant
(*choseong*) jamo are encoded between U+1100 and U+115F, the vowel (*jungseong*)
jamo are encoded between U+1160 and U+11A7, and the optional trailing consonant
(*jongseong*) jamo between U+11A8 and U+11FF. (At least in the primary Hangul
Jamo Unicode block; other jamo are encoded in extension blocks.)
The Hangul shaper will first attempt to compose any sequences of conjoining jamo
into an encoded form in the precomposed syllable block. But where this is not
successful - for example, in an Old Korean form which is not encoded in Unicode
as a precomposed syllable - then the shaper will instead *decompose* any LV
syllables to break the syllable into separate L, V, and T? characters, and then
apply the Korean shaping features (`ljmo`, `vjmo`, `tjmo`) to select forms of
the jamo which are appropriately positioned and sized to combine into the correct
grapheme-image.
For example, the Old Korean syllable ᄒᆞᆯ is not encoded in Unicode as a precomposed
syllable, and so must be encoded with the three individual jamo. The Hangul
shaper applies the `ljmo` feature to the *choseong*, the `vjmo` feature to the
*jungseong* and the `tjmo` feature to the *jongseong*. The resulting sequence
produces a glyph which renders the syllable correctly, with the `vjmo` and
`tjmo` generally producing zero-width mark glyphs positioned appropriately. An
alternative to this technique is to use the `ccmp` feature to turn decomposed
jamo into a precomposed glyph.
For further information, see sections 3.12 and 18.6 of the Unicode Standard.
done: true