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 <!ENTITY name "value"> syntax in a document type definition (DTD) or XML schema. Then, the name defined in the entity declaration is subsequently used in the XML. When used in the XML, it is called an entity reference.
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XML has two relevant concepts:
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 |
| amp | & |
& | x26 (38) | ampersand |
| apos | ' |
' | x27 (39) | apostrophe (= apostrophe-quote) |
| lt | < |
< | x3C (60) | less-than sign |
| gt | > |
> | x3E (62) | greater-than sign |
A "character reference" is a construct such as   or equally   that refers to a character by means of its numeric Unicode code point, i.e. here, the character code 160 (or xA0 in hexa) refers the character, the non-breaking space.