![]() I offer this definition: A grapheme is the smallest distinct component in a written text. It's a word that precisely conjure up the idea of "a graphical unit in a text". Which is the greater entity, the grapheme or the character? What does one call those graphic elements in text that are not letters or punctuation? One term that springs quickly to mind is "grapheme". The problem is that neither are they all characters. Unicode doesn't concern itself much with glyphs, and the things it defines in its code charts are certainly not glyphs. For every character, there is an infinite number of possible glyphs.įirst, as I stated, there is an infinite number of possible glyphs for each character so no, a character is not "always represented by a single glyph". A font provides a set of glyphs for a certain set of characters (not Unicode characters). Unicode normalization addresses this issue.Ī glyph is the visual representation of a character. ![]() This means that there is more than one way in Unicode to represent a character. Unfortunately, the Unicode rules allow some juxtaposed graphemes to be interpreted as other graphemes that already have their own code points ( precomposed forms). Unicode provides rules for the interpretation of juxtaposed graphemes as individual characters.Ī Unicode code point is a unique number assigned to each Unicode character (which is either a character or a grapheme). What the Unicode standard defines as "characters" is actually a mix of graphemes and characters. Outside the Unicode standard a character is an individual unit of text composed of one or more graphemes. A font may contain multiple alternative glyphs for the same grapheme, too. For OTF, the font's GSUB and GPOS tables contain substitution and positioning information to make this work. Fonts may compose multiple glyphs into a single representation, for example, if the above ä is a single code point, a font may choose to render that as two separate, spatially overlaid glyphs. the zero-width non-joiner, or directional overrides).Ī glyph is an image, usually stored in a font (which is a collection of glyphs), used to represent graphemes or parts thereof. Some code points are never part of any grapheme (e.g. ä may be two code points, one for the base character a followed by one for the diaeresis but there's also an alternative, legacy, single code point representing this grapheme). For example, both a and ä are graphemes, but they may consist of multiple code points (e.g. For example, the snowman glyph ( ☃) is a single code point but 3 UTF-8 code units, and 1 UTF-16 code unit.Ī grapheme is a sequence of one or more code points that are displayed as a single, graphical unit that a reader recognizes as a single element of the writing system. A single code unit may represent a full code point, or part of a code point. In UTF-8 this means 8 bits, in UTF-16 this means 16 bits. Each code point is a number which is given meaning by the Unicode standard.Ī code unit is the unit of storage of a part of an encoded code point. ![]() How exactly do each of these concepts differ from each other, and in what circumstances would they not have a one-to-one relationship with each other?Ĭharacter is an overloaded term that can mean many things.Ī code point is the atomic unit of information. So I seek the arcane wisdom of those more learned than I. Most of these definitions possess the quality of sounding very academic and formal, but lack the quality of meaning anything, or else defer the problem of definition to yet another glossary entry or section of the standard. (1) A minimally distinctive unit of writing in the context of a particular writing system. In displaying Unicode character data, one or more glyphs may be selected to depict a particular character. (1) An abstract form that represents one or more glyph images. (3) The basic unit of encoding for the Unicode character encoding. A unit of information used for the organization, control, or representation of textual data.Ĭharacter. The Unicode Consortium offers a glossary to explain this stuff, but it's full of "definitions" like this:Ībstract Character. Seeing how these terms get used in documents like Matthias Bynens' JavaScript has a unicode problem or Wikipedia's piece on Han unification, I've gathered that these concepts are not the same thing and that it's dangerous to conflate them, but I'm kind of struggling to grasp what each term means. In particular, the distinction between code points, characters, glyphs and graphemes - concepts which in the simplest case, when dealing with English text using ASCII characters, all have a one-to-one relationship with each other - is causing me trouble. Trying to understand the subtleties of modern Unicode is making my head hurt.
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