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Tamil OpenType Specification | Terms | Shaping | Features | Other | Appendix


Terms

The following terms are useful for understanding the layout features and script rules discussed in this document.

Base glyph - the only consonant or consonant conjunct in the syllable that is written in its "full" (nominal) form. In "degenerate" syllables that have no vowel (last letter of a word), the last consonant in halant form serves as the base consonant and is mapped as the base glyph. Layout operations are defined in terms of a base glyph, not a base character, since the base can often be a ligature.

Below-base form of consonants - the form in which consonants appear below the base glyph.

Consonant - each represents a single consonant sound. Consonants may exist in different contextual forms, and have an inherent vowel (usually, the short vowel "a"). Therefore, those illustrated in the examples below are named, for example, "Ka" and "Ta", rather than just "K" or "T."

Halant (Virama) - the character used after a consonant to "strip" it of its inherent vowel.

Note: a syllable containing halant characters may be shaped with no visible halant signs by using different consonant forms or conjuncts instead.

Halant form of consonants - form produced by adding the Virama to the nominal shape. The Halant form is used in syllables that have no vowel or as the half form when no distinct shape for the half form exists. In Tamil, the half and halant forms are always the same.

Half form of consonants (pre-base form) - form in which consonants appear to the left of the base consonant, if it does not participate in a ligature. Consonants in their half form, precede the ones forming the base glyph. If a consonant does not have a distinct shape for the half form, and does not form any ligature, it will be displayed with an explicit Virama; that is, in this case, the half form and the halant form have the same shape.

Matra (Dependent Vowel) - used to represent a vowel sound that is not inherent to the consonant. Dependent vowels are referred to as "matras" in Sanskrit. They are always depicted in combination with a single consonant, or with a consonant cluster. The greatest variation among different Indian scripts is found in the rules for attaching dependent vowels to base characters.

Post-base form of consonants - form in which consonants appear to the right of the base glyph.

Pre-base form of consonants - form in which consonants appear to the left of the base glyph.

Tamil syllable - the effective orthographic "unit" of Indic writing systems; consisting of a consonant and a vowel core, and optionally preceded by one or more consonants. Syllables are composed of consonant letters, independent vowels, and dependant vowels. In a text sequence, these characters are stored in phonetic order (although they may not be represented in phonetic order when displayed). Once a syllable is shaped, it is indivisible. The cursor cannot be positioned within the syllable. Transformations discussed in this document do not cross syllable boundaries.

Notation

The following notation is used in this document to illustrate layout operations:

C - a consonant character

K - a "generalized" consonant, including Akhand ligatures.

Ah, Af - the Akhand half and full form respectively

V - the Vattu glyph

Cf, Kf - a glyph representing a full form of a consonant/generalized consonant

Ch, Kh - a half form of a (generalized) consonant

Cs, Ks - a below-base form of a (generalized) consonant

Cp, Kp - a post-base form of a (generalized) consonant

H - a Halant character or glyph

M - a Matra character or glyph

VO - an independent vowel

Lf - a consonant conjunct

Lh - a half form ligature (except Akhand) e.g. a vattu ligature

VM - a vowel modifier character or glyph

SM - a stress or tone mark (e.g. Udatta, Anudatta, Acute, Grave)

LM - a length mark

{ } - indicates 0 or multiple occurrences

[ ] - indicates 0 or 1 occurrence



this page was last updated 20 March 2002
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Tamil OpenType Specification | Terms | Shaping | Features | Other | Appendix
Microsoft Typography | Developer information | Specifications | OpenType font development