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
is always bound to the special XML namespace) is treated as a unique
identifier by compliant applications.
- Learn about some of the reasons for xml:id, as well as some remaining complications, in The xml:id Conundrum by Rich Salz (O'Reilly Media, xml.com, February 2005).
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