1.7 Summary

CTL languages require complex transformations to properly display or print characters. The fundamental characteristics of CTL languages are:

• Bidirectional text--Arabic and Hebrew are written right to left, but numbers and Roman-based characters are written left to right.

• Contextual analysis--each Arabic character has up to four display representations. The representation glyph depends on its position in the text.

• Ligatures--combinations of two or more Arabic characters can form a different, single character.

• Diacritics--diacritical marks placed above, below, or inside vowels and consonants modify their tonal value.

• Character clusters--syllables and cells, especially in Thai, are composed of several alphabetic elements, including vowels, consonants, diacritics, and tone marks.

• Number and date formats--some Arabic countries use Hindi digits rather than Arabic digits, and the Islamic calendar rather than the Western calendar.

Motif interfaces with PLS which interfaces with the CTL language engines. Applications that make use of Motif services need not address CTL issues directly because all CTL transformations and rendering are handled transparently.