Table of contentsAppendices |
1 IntroductionIntroductionThis specification defines the syntax and semantics of the XSLT language. A transformation in the XSLT language is expressed as a well-formed XML document [XML] conforming to the Namespaces in XML Recommendation [XMLNAMES], which may include both elements that are defined by XSLT and elements that are not defined by XSLT. XSLT-defined elements are distinguished by belonging to a specific XML namespace (see [XSLT Namespace]), which is referred to in this specification as the XSLT namespace. Thus this specification is a definition of the syntax and semantics of the XSLT namespace. A transformation expressed in XSLT describes rules for transforming a source tree into a result tree. The transformation is achieved by associating patterns with templates. A pattern is matched against elements in the source tree. A template is instantiated to create part of the result tree. The result tree is separate from the source tree. The structure of the result tree can be completely different from the structure of the source tree. In constructing the result tree, elements from the source tree can be filtered and reordered, and arbitrary structure can be added. A transformation expressed in XSLT is called a stylesheet. This is because, in the case when XSLT is transforming into the XSL formatting vocabulary, the transformation functions as a stylesheet. This document does not specify how an XSLT stylesheet is associated with an XML document. It is recommended that XSL processors support the mechanism described in [XMLSTYLE]. When this or any other mechanism yields a sequence of more than one XSLT stylesheet to be applied simultaneously to a XML document, then the effect should be the same as applying a single stylesheet that imports each member of the sequence in order (see [Stylesheet Import]). A stylesheet contains a set of template rules. A template rule has two parts: a pattern which is matched against nodes in the source tree and a template which can be instantiated to form part of the result tree. This allows a stylesheet to be applicable to a wide class of documents that have similar source tree structures. A template is instantiated for a particular source element to create part of the result tree. A template can contain elements that specify literal result element structure. A template can also contain elements from the XSLT namespace that are instructions for creating result tree fragments. When a template is instantiated, each instruction is executed and replaced by the result tree fragment that it creates. Instructions can select and process descendant source elements. Processing a descendant element creates a result tree fragment by finding the applicable template rule and instantiating its template. Note that elements are only processed when they have been selected by the execution of an instruction. The result tree is constructed by finding the template rule for the root node and instantiating its template. In the process of finding the applicable template rule, more than one template rule may have a pattern that matches a given element. However, only one template rule will be applied. The method for deciding which template rule to apply is described in [Conflict Resolution for Template Rules]. A single template by itself has considerable power: it can create structures of arbitrary complexity; it can pull string values out of arbitrary locations in the source tree; it can generate structures that are repeated according to the occurrence of elements in the source tree. For simple transformations where the structure of the result tree is independent of the structure of the source tree, a stylesheet can often consist of only a single template, which functions as a template for the complete result tree. Transformations on XML documents that represent data are often of this kind (see [Data Example]). XSLT allows a simplified syntax for such stylesheets (see [Literal Result Element as Stylesheet]). When a template is instantiated, it is always instantiated with respect to a current node and a current node list. The current node is always a member of the current node list. Many operations in XSLT are relative to the current node. Only a few instructions change the current node list or the current node (see [Template Rules] and [Repetition]); during the instantiation of one of these instructions, the current node list changes to a new list of nodes and each member of this new list becomes the current node in turn; after the instantiation of the instruction is complete, the current node and current node list revert to what they were before the instruction was instantiated. XSLT makes use of the expression language defined by [XPATH] for selecting elements for processing, for conditional processing and for generating text. XSLT provides two "hooks" for extending the language, one hook for extending the set of instruction elements used in templates and one hook for extending the set of functions used in XPath expressions. These hooks are both based on XML namespaces. This version of XSLT does not define a mechanism for implementing the hooks. See [Extensions]. NOTE: The element syntax summary notation used to describe the syntax of XSLT-defined elements is described in [Notation]. The MIME media types |