xml:id

Give unique identifiers to elements in XML documents

xml:id provides a formal convention for attributes expressing unique identifiers for elements in XML documents. Discover how it avoids the pitfalls of Document Type Definition (DTD) ID types while providing a refreshing simplicity.

Contributors:  W3C

25 April 2007 (First published 06 February 2007)

xml:id provides a formal convention for attributes expressing unique identifiers for elements in XML documents. Discover how it avoids the pitfalls of Document Type Definition (DTD) ID types while providing a refreshing simplicity.

Many XML applications require a mechanism to identify elements. As an example, an ID on an XHTML element is used for linking within a document -- and this is similar to how an anchor name within an HTML document can be used for internal links. DTDs provide a mechanism for asserting that an attribute is of ID type, but DTDs can be problematic in that processors may not address them in all cases. A variety of such complexities has made it difficult to express in a general way which attributes are meant to have ID semantics. xml:id Version 1.0 [W3C Recommendation] is a simple specification expressing the convention that any attribute named xml:id (the xml prefix is always bound to the special XML namespace) is treated as a unique identifier by compliant applications.

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