In SGML, HTML and XML documents, the logical constructs known as character data and attribute values consist of sequences of characters, in which each character can manifest directly (representing itself), or can be represented by a series of characters called a character reference, of which there are two types: a numeric character reference and a character entity reference. This article lists the character entity references that are valid in HTML and XML documents. The Standard Generalized Markup Language (SGML) is a metalanguage in which one can define markup languages for documents. ... HTML, an initialism of Hypertext Markup Language, is the predominant markup language for web pages. ... The Extensible Markup Language (XML) is a general-purpose markup language. ... A numeric character reference (NCR) is a common markup construct used in SGML and other SGML-based 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 (UCS) of Unicode. ... HTML has been in use since 1991 (note that the W3C international standard is now XHTML), but the first standardized version with a reasonably complete treatment of international characters was version 4. ...

An example of a Web browser (Mozilla Firefox) A web browser is a software application that enables a user to display and interact with text, images, videos, music and other information typically located on a Web page at a website on the World Wide Web or a local area network. ...

Character reference overview

A numeric character reference refers to a character by its Universal Character Set/Unicode code point, and uses the format The international standard ISO/IEC 10646 defines the Universal Character Set (UCS) as a character encoding. ... The Unicode Standard, Version 5. ...

&#nnnn;

or

&#xhhhh;

where nnnn is the code point in decimal form, and hhhh is the code point in hexadecimal form. The x must be lowercase in XML documents. The nnnn or hhhh may be any number of digits and may include leading zeros. The hhhh may mix uppercase and lowercase, though uppercase is the usual style. For other uses, see Decimal (disambiguation). ... In mathematics and computer science, hexadecimal, base-16, or simply hex, is a numeral system with a radix, or base, of 16, usually written using the symbols 0–9 and A–F, or a–f. ...

In contrast, a character entity reference refers to a character by the name of an entity which has the desired character as its replacement text. The entity must either be predefined (built-in to the markup language) or explicitly declared in a Document Type Definition (DTD). The format is the same as for any entity reference: An SGML entity is an abbreviation for part of a document. ... Document Type Definition (DTD), defined slightly differently within the XML and SGML (the language XML was derived from) specifications, is one of several SGML and XML schema languages, and is also the term used to describe a document or portion thereof that is authored in the DTD language. ...

&name;

where name is the name of the entity. The semicolon is required.

Predefined entities in XML

Despite the title of this Wikipedia topic, the XML specification does not use the term "character entity" or "character entity reference". The XML specification defines five "predefined entities" representing special characters, and requires that all XML processors honor them. The entities can be explicitly declared in a DTD, as well, but if this is done, the replacement text must be the same as the built-in definitions. XML also allows other named entities of any size to be defined on a per-document basis.

The table below lists the five XML predefined entities. The "Name" column mentions the entity's name. The "Character" column shows the character, if it is renderable. In order to render the character, the format &name; is used; for example, & renders as &. The "Unicode code point" column cites the character via standard UCS/Unicode "U+" notation, which shows the character's code point in hexadecimal. The decimal equivalent of the code point is then shown in parentheses. The "Standard" column indicates the first version of XML that includes the entity. The "Description" column cites the character via its canonical UCS/Unicode name, in English.

Quotation marks or inverted commas (also called quotes and speech marks) are punctuation marks used in pairs to set off speech, a quotation, a phrase or a word. ... An ampersand (&), also commonly called an and sign is a logogram representing the conjunction and. ... For the prime symbol (′) used for feet and inches, see Prime (symbol). ... This article is about inequalities in mathematics. ... This article is about inequalities in mathematics. ...

Character entities in HTML

The HTML 4 DTD explicitly declares 252 character entities. HTML processors must honor the HTML DTD's declarations, even if the DTD is not mentioned in the HTML document. HTML does not allow other named entities to be defined.

HTML document authors who have been exposed to XML and XHTML often overlook the fact that the apos entity is not defined in HTML. rsquo is the best alternative in this case (but it is not the same character), or authors can use a numeric character reference instead (' or ' which always designate the character using the numeric value of its Unicode code point, independantly of the actual document encoding).

In the table below, the HTML built-in character entities are listed. The columns are as in the XML entity table, above, except "Standard" column indicates the first version of HTML that includes the entity. The version is one of the major releases of the HTML spec: 2.0, 3.2, or 4.0. HTML 4.01 didn't introduce any new entities.

^  A blue background has been used in order to display each space's width. This article or section does not cite its references or sources. ... The ß — Eszett [] in German or scharfes Es (sharp es) if spelled out — is a letter used only in the German alphabet. ... The left-to-right mark () is a non-printing character used in the computerized typesetting of bi-directional text containing mixed left-to-right scripts (such as English and Russian) and right-to-left scripts (such as Arabic and Hebrew). ... The right-to-left mark () is a non-printing character used in the computerized typesetting of bi-directional text containing mixed left-to-right scripts (such as English and Russian) and right-to-left scripts (such as Arabic and Hebrew). ... Karl Theodor Wilhelm Weierstraß (October 31, 1815 – February 19, 1897) was a German mathematician who is often cited as the father of modern analysis. (The letter ß may be transliterated as ss; one often writes Weierstrass. ... Fig. ...

Entities representing special characters in XHTML

The XHTML DTDs explicitly declare 252 entities whose expansion is a single character, which can therefore be informally referred to as "character entities". These have the same names and represent the same characters as the 252 character entities in HTML. Also, by virtue of being XML, XHTML documents may reference the predefined ' entity, which is not one of the 252 character entities in HTML. Additional entities of any size may be defined on a per-document basis. However, the usability of entity references in XHTML is affected by how the document is being processed: The Extensible HyperText Markup Language, or XHTML, is a markup language that has the same depth of expression as HTML, but also conforms to XML syntax. ...

• If the document is read by a conforming HTML processor, then only the 252 HTML character entities can safely be used. The use of ' or custom entity references may not be supported and may produce unpredictable results.
• If the document is read by an XML parser that does not or cannot read external entities, then only the five built-in XML character entities can safely be used, although other entities may be used if they are declared in the internal DTD subset.
• If the document is read by an XML parser that does read external entities, then the five built-in XML character entities can safely be used. The other 248 HTML character entities can be used as long as the XHTML DTD is accessible to the parser at the time the document is read. Other entities may also be used if they are declared in the internal DTD subset.

Because of the special ' case mentioned above, only ", &, <, and > will work in all processing situations.

See also

• Character encodings in HTML
• SGML entity

HTML has been in use since 1991, but HTML 4. ... An SGML entity is an abbreviation for part of a document. ...

References

• Unicode Consortium. See also: Unicode Consortium
  • UnicodeData.txt from the Unicode Consortium
• World Wide Web Consortium. See also: World Wide Web Consortium
  • XML 1.0 spec
  • HTML 2.0 spec
  • HTML 3.2 spec
  • HTML 4.0 spec
  • HTML 4.01 spec

In computing, Unicode is the international standard whose goal is to provide the means to encode the text of every document people want to store in computers. ... It has been suggested that W3C Markup Validation Service be merged into this article or section. ...

External links

• HTML entities visual likeness tool
• List of Unicode code points (for numerical references)