Character encoding is the process of assigning numbers to graphical characters, especially the written characters of human language, allowing them to be stored, transmitted, and transformed using digital computers. The numerical values that make up a character encoding are known as "code points" and collectively comprise a "code space", a "code page", or a "character map".
In computing, plain text is a loose term for data that represent only characters of readable material but not its graphical representation nor other objects. It may also include a limited number of "whitespace" characters that affect simple arrangement of text, such as spaces, line breaks, or tabulation characters. Plain text is different from formatted text, where style information is included; from structured text, where structural parts of the document such as paragraphs, sections, and the like are identified; and from binary files in which some portions must be interpreted as binary objects.
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 code, 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:
Windows Notepad is a simple text editor for Windows; it creates and edits plain text documents. First released in 1983 to commercialize the computer mouse in MS-DOS, Notepad has been part of every version of Windows ever since.
Mojibake is the garbled or gibberish text that is the result of text being decoded using an unintended character encoding. The result is a systematic replacement of symbols with completely unrelated ones, often from a different writing system.
A text file is a kind of computer file that is structured as a sequence of lines of electronic text. A text file exists stored as data within a computer file system. In operating systems such as CP/M and DOS, where the operating system does not keep track of the file size in bytes, the end of a text file is denoted by placing one or more special characters, known as an end-of-file (EOF) marker, as padding after the last line in a text file. On modern operating systems such as Microsoft Windows and Unix-like systems, text files do not contain any special EOF character, because file systems on those operating systems keep track of the file size in bytes. Most text files need to have end-of-line delimiters, which are done in a few different ways depending on operating system. Some operating systems with record-orientated file systems may not use new line delimiters and will primarily store text files with lines separated as fixed or variable length records.
A newline is a control character or sequence of control characters in character encoding specifications such as ASCII, EBCDIC, Unicode, etc. This character, or a sequence of characters, is used to signify the end of a line of text and the start of a new one.
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.
The null character is a control character with the value zero. It is present in many character sets, including those defined by the Baudot and ITA2 codes, ISO/IEC 646, the C0 control code, the Universal Coded Character Set, and EBCDIC. It is available in nearly all mainstream programming languages. It is often abbreviated as NUL. In 8-bit codes, it is known as a null byte.
GB 18030 is a Chinese government standard, described as Information Technology — Chinese coded character set and defines the required language and character support necessary for software in China. GB18030 is the registered Internet name for the official character set of the People's Republic of China (PRC) superseding GB2312. As a Unicode Transformation Format, GB18030 supports both simplified and traditional Chinese characters. It is also compatible with legacy encodings including GB2312, CP936, and GBK 1.0.
A variable-width encoding is a type of character encoding scheme in which codes of differing lengths are used to encode a character set for representation, usually in a computer. Most common variable-width encodings are multibyte encodings, which use varying numbers of bytes (octets) to encode different characters. (Some authors, notably in Microsoft documentation, use the term multibyte character set, which is a misnomer, because representation size is an attribute of the encoding, not of the character set.)
This article compares Unicode encodings. Two situations are considered: 8-bit-clean environments, and environments that forbid use of byte values that have the high bit set. Originally such prohibitions were to allow for links that used only seven data bits, but they remain in some standards and so some standard-conforming software must generate messages that comply with the restrictions. Standard Compression Scheme for Unicode and Binary Ordered Compression for Unicode are excluded from the comparison tables because it is difficult to simply quantify their size.
Windows code pages are sets of characters or code pages used in Microsoft Windows from the 1980s and 1990s. Windows code pages were gradually superseded when Unicode was implemented in Windows, although they are still supported both within Windows and other platforms, and still apply when Alt code shortcuts are used.
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:
Character encoding detection, charset detection, or code page detection is the process of heuristically guessing the character encoding of a series of bytes that represent text. The technique is recognised to be unreliable and is only used when specific metadata, such as a HTTP Content-Type: header is either not available, or is assumed to be untrustworthy.
Microsoft was one of the first companies to implement Unicode in their products. Windows NT was the first operating system that used "wide characters" in system calls. Using the UCS-2 encoding scheme at first, it was upgraded to the variable-width encoding UTF-16 starting with Windows 2000, allowing a representation of additional planes with surrogate pairs. However Microsoft did not support UTF-8 in its API until May 2019.
A number of text encoding standards are used on the World Wide Web. The same encodings are used in local files, in fact many more, at least historically. Exact measurements for the prevalence of each are not possible, because of privacy reasons, but rather accurate estimates are available for public web sites, and statistics may reflect use in local files. Attempts at measuring encoding popularity may utilize counts of numbers of (web) documents, or counts weighed by actual use or visibility of those documents.
