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| Microsoft Typography | Developer information | Specifications | OpenType font development | |||
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| Bengali OpenType Specification | Terms | Shaping | Features | Other | Appendix | |||
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The following terms are useful for understanding the layout features and script rules discussed in this document. Akhand ligatures - required consonant ligatures that may appear anywhere in the syllable, and may or may not involve the base glyph. Akhand ligatures have the highest priority and are formed first; some languages include them in their alphabets. Akhand ligatures may be in either half or full or other form. 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. Consonants in below-base form appear in Bengali syllables after the ones that form the base glyph. Below-base forms are represented by the non-spacing mark glyph. Bengali syllable - the effective orthographic "unit" of Bengali 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. 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." Consonant conjuncts - (also referred to as simply conjuncts) ligatures of two or more consonants. Consonant conjuncts may have both full and half forms, or only full forms. Halant (Virama) - the character used after a consonant to "strip" it of its inherent vowel. A Virama follows all but the last consonant in every Bengali syllable.
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 Bengali scripts the half and halant forms are often 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. Nukta - a character that alters the way a preceding consonant is pronounced. Post-base form of consonants - form in which consonants appear to the right of the base glyph. Post-base forms are usually spacing glyphs. Pre-base form of consonants - form in which consonants appear to the left of the base glyph. Reph - the above-base form of the letter "Ra" that is used in most scripts if "Ra" is the first consonant in the syllable and is not the base consonant. In Bengali scripts Reph is an above-base form only. Vattu (Rakar) - the below-base form of letter "Ra". Vattu requires exceptional treatment for two reasons. First, it may become a below-base form to half form glyphs, as well as to full form glyphs. Second, it often assumes different shapes depending on what consonant it follows. Consonants will form required ligatures with Vattu, producing vattu ligatures that can either be in half or full form.
Notation The following notation is used in this document to illustrate layout operations: C - a consonant character K - a "generalized" consonant, including:
"Generalized" consonants are produced by composing akhands and composing ligatures that contain the nukta sign. Ah, Af - the Akhand half and full form respectively V - the Vattu glyph Reph - the Reph 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
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| Bengali OpenType Specification | Terms | Shaping | Features | Other | Appendix | |||
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| Microsoft Typography | Developer information | Specifications | OpenType font development | |||
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