XHTML (Exntensible Hyptertext Markup Language)

XHTML is a reformulation of HTML 4 as an XML application. The XHTML DTDs define elements and attributes as they are in HTML 4.01. XHTML Basic is a smaller subset of XHTML, but otherwise the XHTML 1.x specifications made no changes to the actual vocabulary. XHTML 2.0 adds new features to the XHTML vocabulary. See also HTML, hypertext, markup.

XML declaration

The first element of a document prolog, declaring that the document is an XML document and the XML version it conforms to. Most documents will have this XML declaration as their first line:

<?xml version="1.0"?>

XLink (XML Linking Language)

Specifies elements that can be used in XML documents to create and describe links between resources. XLink provides for more robust linking relationships than do the simple hyperlinks in HTML.

XML processor

A generic term for any program that takes an XML document as input and does something with it. A program that reads an XML document, parses it, and produces formatted output is an XML processor. See also parser.

XML Schema

An alternative to DTDs for document modeling, schemas are written as XML, and like DTDs, define the elements, entities, and content model of documents. Schemas have many additional capabilities such as data type control and content restrictions.

XPath (XML Path Language)

A language used to address parts of an XML document. XPath locator syntax uses core functions based on the node hierarchy of a document, and evaluates expressions to determine a location object. XPath locations are used by XSLT and XPointer.

XPointer (XML Pointer Language)

A special scheme, based on XPath, that identifies locations using special extensions to URIs. XPointer locations support the use of ID attributes for absolute location references in an XML document, and can step through the node hierarchy to find specific elements.

XSL (Extensible Stylesheet Language)

A specification for converting XML documents to formatted results. Extensible Stylesheet Language includes two subspecifications, XSL-FO and XSLT. See also XSLT and See also XSL-FO.


A vocabulary for describing formatted documents, typically for print media.

XSLT (Extensible Stylesheet Language Transformations)

A transformation functions similarly to a stylesheet, except that instead of simply applying formatting rules to elements, it can alter the structure of a document to produce a document with a new structure.