HTML Character Entities

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.

A character entity reference refers to the content of a named entity. An entity declaration is created in XML, SGML and HTML documents (before HTML5) by using the syntax in a document type definition (DTD).

Character reference overview

In HTML and XML, a ''numeric character reference'' refers to a character by its Universal Coded Character Set/Unicode ''code point'', and uses the format:
&#x''hhhh'';
or
&#''nnnn'';
where the x must be lowercase in XML documents, ''hhhh'' is the code point in hexadecimal form, and ''nnnn'' is the code point in decimal form. The ''hhhh'' (or ''nnnn'') may be any number of hexadecimal (or decimal) digits and may include leading zeros. The ''hhhh'' for hexadecimal digits may mix uppercase and lowercase letters, though uppercase is the usual style. However the XML and HTML standards restrict the usable code points to a set of valid values, which is a subset of UCS/Unicode code point values, that excludes all code points assigned to non-characters or to surrogates, and most code points assigned to C0 and C1 controls (with the exception of line separators and tabulations treated as white spaces).

By contrast, a ''character entity reference'' refers to a sequence of one or more characters by the name of an ''entity'' which has the desired characters as its ''replacement text''. The entity must either be predefined (built into the markup language), or otherwise explicitly declared in a Document Type Definition (DTD) (see ). The format is the same as for any entity reference:
&''name'';
where ''name'' is the case-sensitive name of the entity. The semicolon is usually required in the character entity reference, unless marked otherwise in the table below (see ).

Standard public entity sets for characters

; XML: XML specifies five predefined entities needed to support every printable ASCII character: &, <, >, ', and ". The trailing semicolon is mandatory in XML (and XHTML) for these five entities (even if HTML or SGML allows omitting it for some of them, according to their DTD).
; ISO Entity Sets: SGML supplied a comprehensive set of entity declarations for characters widely used in Western technical and reference publishing, for Latin, Greek and Cyrillic scripts. The American Mathematical Society also contributed entities for mathematical characters (see ).
; HTML Entity Sets: Early versions of HTML built in small subsets of these, relating to characters found in three Western 8-bit fonts.
; MathML Entity Sets: The W3C developed a set of entity declarations for MathML characters.
; XML Entity Sets: The W3C MathML Working Group took over maintenance of the ISO public entity sets, combined with the MathML and documents them i
XML Entity Definitions for Characters
This set can support the requirements of XHTML, MathML and as an input to future versions of HTML.
; HTML5: HTML5 adopts the XML entities a
named character references
and does not group them into sets. The character reference names originate from XML Entity Definitions for Characters. The HTML5 specification additionally provides mappings from the names to Unicode character sequences using JSON.

Numerous other entity sets have been developed for special requirements, and for major and minority scripts. However, the advent of Unicode has largely superseded them.

Formal public identifiers for HTML DTD entities subsets

The full formal public identifier and system identifier for the DTD entities subset (where the character entity name is defined) is actually mapped from one of the following three defined named entities:

Formal public identifiers for old ISO entities subsets

The ISO entities subsets are old (documented) character subsets, which are given SGML character entity names in ISO 8879 and ISO 9573, and which were used in legacy encodings before the unification within ISO 10646. Their full formal public identifiers are as follows:

List of character entity references in HTML

HTML5 defines many named entities, references to which act as mnemonic aliases for certain Unicode characters. The HTML5 specification does not allow users to define additional entities, as it no longer accepts any DTD to be referenced or extended inside HTML documents (this is still needed in XHTML, which is based on stricter XML parsing rules but allows referencing or defining a DTD in the document header, because XML does not predefine most HTML entities).

In the below table, the "Standard" column indicates the first version of the HTML DTD that defines the character entity reference, and indicates characters that are predefined in XML without needing any DTD. To use one of these character entity references in an HTML or XML document, enter an ''ampersand'' (&) followed by the ''entity name'', and a ''semicolon'' (mandatory in XML, and strongly recommended in HTML for all entities, even if HTML allows omitting the semicolon only from some entities indicated below by ), e.g., enter © for the copyright symbol .

There are no predefined character entities in HTML for characters or sequences of most scripts encoded in the UCS (except a common subset of whitespace, punctuation, mathematical or technical symbols, currency symbols, a few Hebrew symbols used in mathematical notations, and the most common letters in Latin, Greek or Cyrillic). Note also that ''not all'' bidirectional controls defined in UCS/Unicode are represented as standard character entities in HTML (not even in HTML5, which defines more general directional elements and attributes for that purpose). Notably, there are no predefined HTML character entities for controls that were added in the UCS/Unicode and formally defined in version 2 of the Unicode Bidi Algorithm.

Most entities are predefined in XML and HTML to reference just one character in the UCS, but there are no predefined entities for isolated combining characters, variation selectors, or characters for private use assignments; however the list includes some predefined entities for character sequences of two characters containing some of them. Since HTML 5.0 (and MathML 3.0 which shares the same set en entities), all entities are encoded in Unicode normalization forms C and KC (this was not the case with older versions of HTML and MathML, so older entities that were initially defined with characters for private use assignments, CJK compatibility forms, or in non-NFC forms were modified).

However, all valid characters and sequences in the UCS, including all bidirectional controls or private-use assignments (but with the exception of non-whitespace C0 and C1 controls, non-characters, and surrogates) are also usable and valid in HTML, XML, XHTML and MathML, either in plain-text values of attributes or in text elements (by encoding them directly as plain text, or using numeric character references when needed).

Notes

Entities representing special characters in XHTML

The XHTML DTDs explicitly declare 253 entities (including the 5 predefined entities of XML 1.0) whose expansion is a single character, which can therefore be informally referred to as "character entities". These (with the exception of the ' entity) have the same names and represent the same characters as the 252 character entities in HTML 4.0. Also, by virtue of being XML, XHTML documents may reference the predefined ' entity, which is not one of the 252 character entities in HTML 4.0. 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:

* Legacy abbreviated character entities (without the final colon) inherited from HTML 2.0 (and still supported in HTML 5.0) are not supported in XML 1.0 and XHTML; the trailing semicolon must be present in all entity references used in XML and XHTML documents.
* If the XHTML document is read by a conforming HTML 4.0 processor, then only the 252 HTML 4.0 character entities may safely be used. The use of ' or custom entity references may not be supported and may produce unpredictable results (it is recommended to use the numerical character reference ' instead).
* 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. However, modern XML parsers recognize and implement a builtin cache for SGML references to DTDs used by all standard versions of HTML, XHTML, SVG and MathML, without needing to parse and process the external DTD via their URL and without needing to process entities defined in an internal DTD subset of the document.
* If the document is read by an XML parser that does read external entities and does not implement a builtin cache for well-known DTDs, then the five built-in XML character entities (and numeric character references) 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 and the XML processor can parse internal DTD subsets.
* HTML 5.0 parsers cannot process XHTML documents, and it's impossible to define a fully validating DTD for HTML5 documents encoded with the XHTML syntax (notably it's impossible to validate all attributes names, notably "data-*" attributes); as well it's still impossible to fully validate (with W3C standard schemas for XML, such as XSD or relax NG) HTML5 documents represented in the XHTML syntax, and for now a custom validator specific to HTML 5.0 is required.

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

See also

* Character encodings in HTML
* Digraph and Trigraph, a similar concept to enter unavailable characters
* Escape character
* HTML decimal character rendering
* Percent-encoding, used in URLs
* SGML entity

References

Further reading

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 3.2 spec
*
HTML 4.0 spec
*
HTML 4.01 spec
*
HTML 5 spec
*
XHTML 1.0 spec
*
XML Entity Definitions for Characters
* The normative reference to RFC 2070 (still found in DTDs defining the character entities for HTML or XHTML) is historic; this RFC (along with other RFC's related to different part of the HTML specification) has been deprecated in favor of the newer informational RFC 2854 which defines the "text/html" MIME type and references directly the W3C specifications for the actual HTML content.
* Numerical Reference of Unicode code points at Wikibooks

W3 HTML5 Character Reference Chart

External links

at the W3C

{{Webarchive, url=https://web.archive.org/web/20180129004522/http://www.html-entities.org/ , date=29 January 2018

XML and HTML character entity references
HTML
XML
Unicode