In comparison, modern displays for Arabic text select appropriate, context-dependent font glyphs for each text element, which means that they transform text into a glyph vector. Since the Arabic script is cursive, connecting adjacent letters to each other, computers select images for each letter based on the surrounding letters. In Unicode , on the other hand, letters are normally stored abstract, and a display system is expected to select the necessary glyphs. They were included for interoperability with legacy systems and codepages, and for unsophisticated display systems. By default, this means that the destination buffer may receive text with a length different from the source length.
Some legacy systems rely on the length of the text to be constant.
They expect extra spaces to be added or consumed either next to the affected character or at the end of the text. The number of UChars in source . The destination buffer that will receive the results of the requested operations. It may be NULL only if destSize is 0. The source and destination must not overlap.