List of XML and HTML character entity references

A character entity reference refers to the content of a named entity. An entity declaration is created by using the <!ENTITY name "value"> syntax in a Document Type Definition (DTD).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.

Contents

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• 1 Character reference overview
• 2 Standard public entity sets for characters
• 3 Predefined entities in XML
• 4 Character entity references in HTML
• 5 Entities representing special characters in XHTML
• 6 See also
• 7 References
• 8 External links

Character reference overview[edit]

A numeric character reference refers to a character by its Universal Character Set/Unicode code point, and uses the format

&#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.

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 into the markup language) or explicitly declared in a Document Type Definition (DTD). The format is the same as for any entity reference:

&name;

where name is the case-sensitive name of the entity. The semicolon is required.

Standard public entity sets for characters[edit]

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.

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 in XML Entity Definitions for Characters. This set can support the requirements of XHTML, MathML and as an input to future versions of HTML.

HTML 5: HTML5 adopts the XML entities as named character references, however it restates them without reference to their sources and does not group them into sets. The HTML 5 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.

Predefined entities in XML[edit]

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. 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.

Character entity references in HTML[edit]

The HTML 4 DTDs define 252 named entities, references to which act as mnemonic aliases for certain Unicode characters. The HTML 4 specification requires the use of the standard DTDs and does not allow users to define additional entities.

In the table below, the "Standard" column indicates the first version of the HTML DTD that defines the character entity reference. HTML 4.01 does not provide any new character references.

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, e.g., &

Notes:

1. Jump up^ DTD: the full public DTD name (where the character entity name is defined) is actually mapped from one of the following three defined named entities:
   • HTMLlat1 maps to:
     • PUBLIC "-//W3C//ENTITIES Latin 1//EN//HTML" in HTML (the DTD is implicitly defined, no system URI is needed);
     • PUBLIC "-//W3C//ENTITIES Latin 1 for XHTML//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml-lat1.ent" in XHTML 1.0;
   • HTMLsymbol maps to:
     • PUBLIC "-//W3C//ENTITIES Symbols//EN//HTML" in HTML (the DTD is implicitly defined, no system URI is needed);
     • PUBLIC "-//W3C//ENTITIES Symbols for XHTML//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml-symbol.ent" in XHTML 1.0;
   • HTMLspecial maps to:
     • PUBLIC "-//W3C//ENTITIES Special//EN//HTML" in HTML (the DTD is implicitly defined, no system URI is needed);
     • PUBLIC "-//W3C//ENTITIES Special for XHTML//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml-special.ent" in XHTML 1.0.
2. Jump up^ Old ISO subset: these are old (documented) character subsets used in legacy encodings before the unification within ISO 10646.
3. Jump up^ Description: the standard ISO 10646 and Unicode character name is displayed first for each character, with non-standard but legacy synonyms shown in italics between parentheses after an equal sign.
4. ^ Jump up to:^a b c d spaces: a blue background is used to display each space‘s width.
5. ^ Jump up to:^a b ligature: this is a standard misnomer as this is a separate character in some languages.
6. ^ Jump up to:^{a b c d e} black: here it seems to mean filled as opposed to hollow.
7. ^ Jump up to:^a b ISO proposed: these characters have been standardized in ISO 10646 after the release of HTML 4.0.
8. Jump up^ alefsym: ‘alef symbol‘ is not the same as U+05D0 ‘Hebrew letter alef‘, although the same glyph could be used to depict both characters.
9. Jump up^ lArr: ISO 10646 does not say that ‘leftwards double arrow‘ is the same as the ‘is implied by‘ arrow, but also does not have any other character for that function. So lArr can be used for ‘is implied by‘ as ISOtech suggests.
10. Jump up^ rArr: ISO 10646 does not say that ‘rightwards double arrow‘ is the ‘implies‘ character but does not have another character with this function, so rArr can be used for ‘implies‘ as ISOtech suggests.
11. Jump up^ prod: ‘n-ary product‘ is not the same character as U+03A0 ‘Greek capital letter Pi‘ though the same glyph might be used for both.
12. Jump up^ sum: ‘n-ary summation‘ is not the same character as U+03A3 ‘Greek capital letter Sigma‘ though the same glyph might be used for both.
13. Jump up^ sim: ‘tilde operator‘ is not the same character as U+007E ‘tilde‘, although the same glyph might be used to represent both.
14. Jump up^ sup: note that nsup, U+2283 ‘not a superset of‘, is not covered by the Symbol font encoding and is not included. Should it be, for symmetry? It is in the ISOamsn subset.
15. Jump up^ perp: Unicode only defines U+22A5 as the "up tack". The Unicode symbol for "perpendicular" is U+27C2. The two symbols look similar, but are separate in Unicode. However, HTML uses U+22A5 as its "perpendicular" symbol. This is a discrepancy between HTML and Unicode. As well, the U+22A4 character (the "down tack" symbol) rendered in a browser such as Firefox 3.6 can match the font of either "up tack" or "perpendicular", but not both, depending on whether a fixed-width or a proportional font is used. When viewed in Firefox 3.6, the symbols rendered in the order U+22A5, U+22A4, U+27C2 in a proportional font: ⊥ ? ? and a fixed width one: ⊥ ? ?, shows that the "down tack" has a similar look to U+22A5 (HTML‘s "perpendicular") in the first case but matches U+27C2 in the second. This exemplifies the difficulties of the semiotics involved in interpreting glyphs, symbols and characters generally.
16. Jump up^ sdot: ‘dot operator‘ is not the same character as U+00B7 ‘middle dot‘.
17. Jump up^ lang: U+2329 ‘left-pointing angle bracket‘ is not the same character as U+003C ‘less than‘, U+2039 ‘single left-pointing angle quotation mark‘, U+27E8 ‘mathematical left angle bracket‘, or U+3008 ‘left angle bracket‘. In HTML 5.0, lang has been remapped to U+27E8 ‘mathematical left angle bracket‘, as U+2329 ‘left-pointing angle bracket‘ has been marked deprecated in Unicode (Unicode.org - Proposal for Additional Deprecated Characters).
18. Jump up^ rang: U+232A ‘right-pointing angle bracket‘ is not the same character as U+003E ‘greater than‘, U+203A ‘single right-pointing angle quotation mark‘, U+27E9 ‘mathematical right angle bracket‘, or U+3009 ‘right angle bracket‘. In HTML 5.0, lang has been remapped to U+27E9 ‘mathematical right angle bracket‘, as U+232A ‘right-pointing angle bracket‘ has been marked deprecated in Unicode (Unicode.org - Proposal for Additional Deprecated Characters).

Entities representing special characters in XHTML[edit]

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. 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:

• 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 (see above) 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[edit]

• Character encodings in HTML
• HTML decimal character rendering
• SGML entity

References[edit]

• 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
  • HTML5 Working Draft
  • 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

External links[edit]

• Character entity references in HTML 4 at the W3C