Extensible Stylesheet Language: Transformations. XSLT is a language for transforming the structure of an XML document. XSLT is designed for use as part of XSL, the stylesheet language for XML. A transformation expressed in XSLT describes a sequence of template rules for transforming a source tree into a result tree; elements from the source tree can be filtered and reordered, and a different structure can be added. A template rule has two parts: a pattern that is matched against nodes in the source tree; and a template that can be instantiated to form part of the result tree. This makes XSLT a declarative language because it is possible to specify what output should be produced when specific patterns occur in the input, which distinguishes it from procedural programming languages, where it is necessary to specify what tasks have to be performed in what order. XSLT makes use of the expression language defined by XPath (a language for addressing the parts of an XML document) for selecting elements for processing, for conditional processing, and for generating text.