Character entity reference
Encyclopedia
In the markup languages SGML, HTML
, XHTML
and XML
, a character entity reference is a reference to a particular kind of named entity
that has been predefined or explicitly declared in a Document Type Definition
(DTD). The "replacement text" of the entity consists of a single character
from the Universal Character Set
/Unicode
. The purpose of a character entity reference is to provide a way to refer to a character that is not universally encodable
.
Although in popular usage character references are often called "entity references" or even "entities", this usage is wrong. A character reference is a reference to a character, not to an entity. Entity reference refers to the content of a named entity. An entity declaration is created by using the
code point
, i.e. here, the character code
) refers the
.
HTML
HyperText Markup Language is the predominant markup language for web pages. HTML elements are the basic building-blocks of webpages....
, XHTML
XHTML
XHTML is a family of XML markup languages that mirror or extend versions of the widely-used Hypertext Markup Language , the language in which web pages are written....
and XML
XML
Extensible Markup Language is a set of rules for encoding documents in machine-readable form. It is defined in the XML 1.0 Specification produced by the W3C, and several other related specifications, all gratis open standards....
, a character entity reference is a reference to a particular kind of named entity
SGML entity
In the Standard Generalized Markup Language , an entity is a primitive data type, which associates a string with either a unique alias or an SGML reserved word . Entities are foundational to the organizational structure and definition of SGML documents...
that has been predefined or explicitly declared in a Document Type Definition
Document Type Definition
Document Type Definition is a set of markup declarations that define a document type for SGML-family markup languages...
(DTD). The "replacement text" of the entity consists of a single character
Character (computing)
In computer and machine-based telecommunications terminology, a character is a unit of information that roughly corresponds to a grapheme, grapheme-like unit, or symbol, such as in an alphabet or syllabary in the written form of a natural language....
from the Universal Character Set
Universal Character Set
The Universal Character Set , defined by the International Standard ISO/IEC 10646, Information technology — Universal multiple-octet coded character set , is a standard set of characters upon which many character encodings are based...
/Unicode
Unicode
Unicode is a computing industry standard for the consistent encoding, representation and handling of text expressed in most of the world's writing systems...
. The purpose of a character entity reference is to provide a way to refer to a character that is not universally encodable
Character encoding
A character encoding system consists of a code that pairs each character from a given repertoire with something else, such as a sequence of natural numbers, octets or electrical pulses, in order to facilitate the transmission of data through telecommunication networks or storage of text in...
.
Although in popular usage character references are often called "entity references" or even "entities", this usage is wrong. A character reference is a reference to a character, not to an entity. Entity reference refers to the content of a named entity. An entity declaration is created by using the
Predefined entity
A "predefined entity reference" is a reference to one of the special characters denoted by:| name | value | character | code (dec) | meaning |
|---|---|---|---|---|
| quot | " |
" | x22 (34) | (double) quotation mark Quotation mark Quotation marks or inverted commas are punctuation marks at the beginning and end of a quotation, direct speech, literal title or name. Quotation marks can also be used to indicate a different meaning of a word or phrase than the one typically associated with it and are often used to express irony... |
| amp | & |
& | x26 (38) | ampersand Ampersand An ampersand is a logogram representing the conjunction word "and". The symbol is a ligature of the letters in et, Latin for "and".-Etymology:... |
| apos | ' |
' | x27 (39) | apostrophe Apostrophe The apostrophe is a punctuation mark, and sometimes a diacritic mark, in languages that use the Latin alphabet or certain other alphabets... (= apostrophe-quote) |
| lt | < |
< | x3C (60) | less-than sign |
| gt | > |
> | x3E (62) | greater-than sign Greater-than sign -Computing:The greater-than sign is an original ASCII character .-Angle brackets:The greater-than sign is used for an approximation of the closing angle bracket . ASCII does not have angular brackets.-Programming language:... |
Character coding
A "character reference" is a construct such as  or equally   that refers to a character by means of its numeric UnicodeUnicode
Unicode is a computing industry standard for the consistent encoding, representation and handling of text expressed in most of the world's writing systems...
code point
Code point
In character encoding terminology, a code point or code position is any of the numerical values that make up the code space . For example, ASCII comprises 128 code points in the range 0hex to 7Fhex, Extended ASCII comprises 256 code points in the range 0hex to FFhex, and Unicode comprises 1,114,112...
, i.e. here, the character code
160 (or xA0 in hexaHexadecimal
In mathematics and computer science, hexadecimal is a positional numeral system with a radix, or base, of 16. It uses sixteen distinct symbols, most often the symbols 0–9 to represent values zero to nine, and A, B, C, D, E, F to represent values ten to fifteen...
) refers the
character, the non-breaking spaceNon-breaking space
In computer-based text processing and digital typesetting, a non-breaking space or no-break space is a variant of the space character that prevents an automatic line break at its position. In certain formats , it also prevents the “collapsing” of multiple consecutive whitespace characters into a...
.
See also
- SGML entitySGML entityIn the Standard Generalized Markup Language , an entity is a primitive data type, which associates a string with either a unique alias or an SGML reserved word . Entities are foundational to the organizational structure and definition of SGML documents...
- Character encodings in HTMLCharacter encodings in HTMLHTML has been in use since 1991, but HTML 4.0 was the first standardized version where international characters were given reasonably complete treatment...
- Numeric character referenceNumeric character referenceA numeric character reference is a common markup construct used in SGML and other SGML-related markup languages such as HTML and XML. It consists of a short sequence of characters that, in turn, represent a single character from the Universal Character Set of Unicode...
- List of XML and HTML character entity references