The Arabic alphabet, or Arabic abjad, is the Arabic script as specifically codified for writing the Arabic language. It is written from right-to-left in a cursive style, and includes 28 letters, of which most have contextual letterforms. The Arabic alphabet is considered an abjad, with only consonants required to be written; due to its optional use of diacritics to notate vowels, it is considered an impure abjad.
A glyph is any kind of purposeful mark. In typography, a glyph is "the specific shape, design, or representation of a character". It is a particular graphical representation, in a particular typeface, of an element of written language. A grapheme, or part of a grapheme, or sometimes several graphemes in combination can be represented by a glyph.
Unicode, formally The Unicode Standard, is a text encoding standard maintained by the Unicode Consortium designed to support the use of text written in all of the world's major writing systems. Version 15.1 of the standard defines 149813 characters and 161 scripts used in various ordinary, literary, academic, and technical contexts.
Web pages authored using HyperText Markup Language (HTML) may contain multilingual text represented with the Unicode universal character set. Key to the relationship between Unicode and HTML is the relationship between the "document character set", which defines the set of characters that may be present in an HTML document and assigns numbers to them, and the "external character encoding", or "charset", used to encode a given document as a sequence of bytes.
UTF-8 is a variable-length character encoding standard used for electronic communication. Defined by the Unicode Standard, the name is derived from Unicode Transformation Format – 8-bit.
UTF-16 (16-bit Unicode Transformation Format) is a character encoding capable of encoding all 1,112,064 valid code points of Unicode (in fact this number of code points is dictated by the design of UTF-16). The encoding is variable-length, as code points are encoded with one or two 16-bit code units. UTF-16 arose from an earlier obsolete fixed-width 16-bit encoding now known as UCS-2 (for 2-byte Universal Character Set), once it became clear that more than 216 (65,536) code points were needed, including most emoji and important CJK characters such as for personal and place names.
The byte order mark (BOM) is a particular usage of the special Unicode character, U+FEFFZERO WIDTH NO-BREAK SPACE, whose appearance as a magic number at the start of a text stream can signal several things to a program reading the text:
UTF-7 is an obsolete variable-length character encoding for representing Unicode text using a stream of ASCII characters. It was originally intended to provide a means of encoding Unicode text for use in Internet E-mail messages that was more efficient than the combination of UTF-8 with quoted-printable.
In word processing and digital typesetting, a non-breaking space, also called NBSP, required space, hard space, or fixed space, is a space character that prevents an automatic line break at its position. In some formats, including HTML, it also prevents consecutive whitespace characters from collapsing into a single space. Non-breaking space characters with other widths also exist.
Apple Symbols is a font introduced in Mac OS X 10.3 “Panther”. This is a TrueType font intended to provide coverage for characters defined as symbols in the Unicode Standard. It continues to ship with Mac OS X as part of the default installation. Prior to Mac OS X 10.5, its path was /Library/Fonts/Apple Symbols.ttf. From Mac OS X 10.5 onward, it is to be found at /System/Library/Fonts/Apple Symbols.ttf, meaning it is now considered an essential part of the system software, not to be deleted by users.
In Unicode, a Private Use Area (PUA) is a range of code points that, by definition, will not be assigned characters by the Unicode Consortium. Three private use areas are defined: one in the Basic Multilingual Plane, and one each in, and nearly covering, planes 15 and 16. The code points in these areas cannot be considered as standardized characters in Unicode itself. They are intentionally left undefined so that third parties may define their own characters without conflicting with Unicode Consortium assignments. Under the Unicode Stability Policy, the Private Use Areas will remain allocated for that purpose in all future Unicode versions.
The hyphen-minus symbol - is the form of hyphen most commonly used in digital documents. On most keyboards, it is the only character that resembles a minus sign or a dash so it is also used for these. The name hyphen-minus derives from the original ASCII standard, where it was called hyphen–(minus). The character is referred to as a hyphen, a minus sign, or a dash according to the context where it is being used.
The Unicode Consortium and the ISO/IEC JTC 1/SC 2/WG 2 jointly collaborate on the list of the characters in the Universal Coded Character Set. The Universal Coded Character Set, most commonly called the Universal Character Set, is an international standard to map characters, discrete symbols used in natural language, mathematics, music, and other domains, to unique machine-readable data values. By creating this mapping, the UCS enables computer software vendors to interoperate, and transmit—interchange—UCS-encoded text strings from one to another. Because it is a universal map, it can be used to represent multiple languages at the same time. This avoids the confusion of using multiple legacy character encodings, which can result in the same sequence of codes having multiple interpretations depending on the character encoding in use, resulting in mojibake if the wrong one is chosen.
Specials is a short Unicode block of characters allocated at the very end of the Basic Multilingual Plane, at U+FFF0–FFFF. Of these 16 code points, five have been assigned since Unicode 3.0:
Many scripts in Unicode, such as Arabic, have special orthographic rules that require certain combinations of letterforms to be combined into special ligature forms. In English, the common ampersand (&) developed from a ligature in which the handwritten Latin letters e and t were combined. The rules governing ligature formation in Arabic can be quite complex, requiring special script-shaping technologies such as the Arabic Calligraphic Engine by Thomas Milo's DecoType.
The zero-width space (), abbreviated ZWSP, is a non-printing character used in computerized typesetting to indicate word boundaries to text-processing systems for scripts that do not use explicit spacing, or after characters not followed by a visible space after which there may be a line break.
The Unicode Standard assigns various properties to each Unicode character and code point.
In Unicode, characters can have a unique name. A character can also have one or more alias names. An alias name can be an abbreviation, a C0 or C1 control name, a correction, an alternate name or a figment. An alias too is unique over all names and aliases, and therefore identifying.
