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XML entity references
There are two additional ways in XML documents to reference characters:
- a numeric character reference refers to a character
- an entity reference refers to a series of characters
Where entities are used, the referenced characters appear.
Numeric character references:
A numeric character reference can be specified in two formats:
&#nnnn; or &#xhhhh;
where the n decimal digits or the h hexadecimal characters identify the Unicode character code of the referenced character.
&#nnnn; or &#xhhhh;
where the n decimal digits or the h hexadecimal characters identify the Unicode character code of the referenced character.
Entity references:
An entity reference is an alternative name for a series of characters.
You can use an entity in the &name; format, where name is the name of the entity.
There are some predefined entities in XML, furthermore you can declare entities in a DTD (Document Type Definition).
Predefined entities:
The following predefined entities exist in XML:| Entity name | Character | Decimal reference | Hexadecimal reference |
|---|---|---|---|
| quot | " | " | " |
| amp | & | & | & |
| apos | ' | ' | ' |
| lt | < | < | < |
| gt | > | > | > |
Declaring entities:
You can declare entities in a DTD in the following format:
<!ENTITY name "text">
where name is the name of the entity and text is the referenced text that appears where the entity is used.
Example 1:
This example declares an entity named 'dotto' and uses it and the predefined 'lt' entity in an XML document:
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<?xml version="1.0" encoding="utf-8"?> <!DOCTYPE sample [ <!NOTATION vrml PUBLIC "VRML 1.0"> <!ENTITY dotto "Dottoro"> ]> <entityTest> <predefined>2 < 5</predefined> <declared>&dotto;</declared> </entityTest> |
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The document tree of the previous example:
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<entityTest> <predefined>2 < 5</predefined> <declared>Dottoro</declared> </entityTest> |
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