Universal Character Set Characters - Characters Grapheme Clusters and Glyphs

Characters Grapheme Clusters and Glyphs

Whereas many other character sets assign a character for every, possible glyph representation of the character, Unicode seeks to treat characters separate from glyphs. This distinction is not always unambiguous, however a few examples will help illustrate the distinction. Often two characters may be combined together to typographically improve the readability of the text. For example, the three letter sequence "ffi", may be treated as a single glyph. Other characters sets would often assign a code point to this glyph in addition to the individual letters: "f" and "i".

In addition, Unicode approaches diacritic modified letters as separate characters that, when rendered, become a single glyph. For example, an "o" with diaeresis: "ö". Traditionally, other character sets assigned a unique character code point for each diacritic modified letter used in each language. Unicode seeks to create a more flexible approach by allowing combining diacritic characters to combine with any letter. This has the potential to significantly reduce the number of active code points needed for the character set. As an example, consider a language that uses the Latin script and combines the diaeresis with the upper- and lower-case letters "a", "o", and "u". With the Unicode approach, only the diaeresis diacritic character needs to be added to the character set to use with the Latin letters: "a", "A", "o", "O", "u", and "U": seven characters in all. A legacy character sets needs to add six precomposed letters with a diaeresis in addition to the six code points it uses for the letters without diaeresis: twelve character code points in total.