View source for XSLT

{{short description|Language for transforming XML documents}}
{{Infobox programming language
| name = XSLT
| logo = 
| logo caption = 
| screenshot = 
| screenshot caption = 
| file ext = .xslt
| paradigm = [[Declarative programming|Declarative]]
| scope = 
| year = 1998
| designer = 
| developer = [[World Wide Web Consortium]] (W3C)
| latest release version = 3.0
| latest release date = {{release date and age|2017|6|8}}
| latest preview date = <!-- {{start date and age|2014|10|2}} -->
| typing = 
| implementations = [[libxslt]], [[Saxon XSLT|Saxon]], [[Xalan]]
| influenced by = [[DSSSL]]
| influenced = 
| programming language = 
| platform = 
| operating system = 
| license = 
| website = {{URL|https://www.w3.org/TR/xslt-30/}}
| wikibooks = 
}}
{{Infobox file format
| name = XSLT
| icon = 
| extension = <code>.xslt</code>
| mime = application/xslt+xml
| uniform type = org.w3.xsl
| owner = 
| genre =
| url = 
| containerfor = 
| containedby = 
| extendedfrom =
| extendedto =
}}
'''XSLT''' ('''Extensible Stylesheet Language Transformations''') is a language originally designed for [[XML transformation language|transforming]] [[XML]] documents into other XML documents,<ref name="Transformation">{{cite web|url=https://www.w3.org/standards/xml/transformation |title=Transformation|date=2012-09-19}}</ref> or other formats such as [[HTML]] for [[web page]]s, [[plain text]], or [[XSL Formatting Objects]]. These formats can be subsequently converted to formats such as [[Portable Document Format|PDF]], [[PostScript]], and [[Portable Network Graphics|PNG]].<ref>{{cite web|url=https://www.w3.org/TR/xslt#output |title=XML Output Method|date=2012-09-19}}</ref> Support for JSON and plain-text transformation was added in later updates to the XSLT 1.0 specification.

XSLT 3.0 implementations support Java, .NET, C/C++, Python, PHP and NodeJS. An XSLT 3.0 JavaScript library can also be hosted within the web browser. Modern web browsers also include native support for XSLT 1.0.<ref name="Used for">{{cite web|url=https://www.w3.org/standards/xml/transformation#uses|title=What is XSLT Used For?|date=2018-02-07}}</ref>

The XSLT document transformation specifies how to transform an XML document into new document (usually XML, but other formats, such as plain text are supported).<ref>{{cite web | url=https://www.w3.org/TR/xslt#section-Introduction | title=Introduction | publisher=W3C | work=XSL Transformations (XSLT) Version 1.0 W3C Recommendation | date=16 November 1999 | access-date=November 7, 2012}}</ref> Typically, input documents are XML files, but anything from which the processor can build an [[XQuery and XPath Data Model]] can be used, such as [[relational database]] tables or [[geographical information systems]].<ref name="Transformation"/>

While XSLT was originally designed as a special-purpose language for XML transformation, the language is [[Turing completeness|Turing-complete]], making it theoretically capable of arbitrary computations.<ref>[https://www.researchgate.net/publication/221568016_XSLT_Version_20_Is_Turing-Complete_A_Purely_Transformation_Based_Proof XSLT Version 2.0 Is Turing-Complete: A Purely Transformation Based Proof]</ref>

==History==
XSLT is influenced by [[functional programming|functional languages]],<ref>{{cite web | url=https://www.ibm.com/developerworks/library/x-xslt/ | author=Michael Kay | title=What kind of language is XSLT? | website=[[IBM]] | access-date=July 8, 2016}}</ref> and by text-based pattern matching languages like [[SNOBOL]] and [[AWK]]. Its most direct predecessor is [[DSSSL]], which did for [[SGML]] what XSLT does for XML.<ref>{{cite web | url=https://www.w3.org/TR/NOTE-XSL.html | title=A Proposal for XSL | publisher=W3C | access-date=November 7, 2012}}</ref>
* XSLT 1.0: XSLT was part of the [[World Wide Web Consortium]] (W3C)'s [[Extensible Stylesheet Language|eXtensible Stylesheet Language]] (XSL) development effort of 1998–1999, a project that also produced [[XSL-FO]] and [[XPath]]. Some members of the standards committee that developed XSLT, including [[James Clark (XML expert)|James Clark]], the editor, had previously worked on DSSSL. XSLT 1.0 was published as a [[W3C recommendation]] in November 1999.<ref name="timelinehistory">{{cite web |url=http://www.dblab.ntua.gr/~bikakis/XML%20and%20Semantic%20Web%20W3C%20Standards%20Timeline-History.pdf |title=XML and Semantic Web W3C Standards Timeline |access-date=2012-02-04 |archive-date=2013-04-24 |archive-url=https://web.archive.org/web/20130424125723/http://www.dblab.ntua.gr/~bikakis/XML%20and%20Semantic%20Web%20W3C%20Standards%20Timeline-History.pdf |url-status=dead }}</ref> Despite its age, XSLT 1.0<ref>{{cite web|url=https://www.w3.org/TR/xslt |title=XSL Transformations (XSLT) |publisher=W3.org |date=1999-11-16 |access-date=2014-07-12}}</ref> is still widely used ({{as of|2018|lc=y}}), since later versions are not supported natively in [[web browser]]s or for environments like [[LAMP (software bundle)|LAMP]].

* XSLT 2.0: after an abortive attempt to create a version 1.1 in 2001,<ref>{{cite web|url=https://www.w3.org/TR/xslt11/ |title=XSL Transformations (XSLT) Version 1.1 |publisher=W3.org |date=2001-08-24 |access-date=2014-07-12}}</ref> the XSL working group joined forces with the [[XQuery]] working group to create [[XPath 2.0]],<ref>{{cite web|url=https://www.w3.org/TR/xpath20/ |title=XML Path Language (XPath) 2.0 (Second Edition) |publisher=W3.org |date=2010-12-14 |access-date=2014-07-12}}</ref> with a richer data model and type system based on [[XML Schema (W3C)|XML Schema]]. Building on this is XSLT 2.0,<ref>{{cite web|url=https://www.w3.org/TR/xslt20/ |title=XSL Transformations (XSLT) Version 2.0 |publisher=W3.org |date=2007-01-23 |access-date=2014-07-12}}</ref> developed under the editorship of [[Michael Howard Kay|Michael Kay]], which reached recommendation status in January 2007.<ref>{{cite web|url=http://www.dblab.ntua.gr/~bikakis/XML%20and%20Semantic%20Web%20W3C%20Standards%20Timeline-History.pdf|title=XML and Semantic Web W3C Standards Timeline|date=2012-02-04|access-date=2012-02-04|archive-date=2013-04-24|archive-url=https://web.archive.org/web/20130424125723/http://www.dblab.ntua.gr/~bikakis/XML%20and%20Semantic%20Web%20W3C%20Standards%20Timeline-History.pdf|url-status=dead}}</ref> The most important innovations in XSLT 2.0 include:
** String manipulation using [[regular expressions]]
** Functions and operators for manipulating dates, times, and durations
** Multiple output documents
** Grouping (creating hierarchic structure from flat input sequences)
** A richer type system and stronger type checking

* XSLT 3.0: became a W3C Recommendation on 8 June 2017. The main new features are:<ref name=new-in-3>{{cite web|title=What's New in XSLT 3.0?
|url=https://www.w3.org/TR/xslt-30/#whats-new-in-xslt3|publisher=w3|access-date=6 January 2014}}</ref> 
** [[Streaming XML|Streaming transformations]]: in previous versions the entire input document had to be read into memory before it could be processed,<ref>
{{cite web|last=Kay|first=Michael|title=A Streaming XSLT Processor|url=https://www.balisage.net/Proceedings/vol5/html/Kay01/BalisageVol5-Kay01.html|publisher=Balisage: The Markup Conference 2010 Proceedings|access-date=15 February 2012}}</ref> and output could not be written until processing had finished. XSLT 3.0 allows [[Streaming XML|XML streaming]] which is useful for processing documents too large to fit in memory or when transformations are chained in [[XML Pipelines]].
** Packages, to improve the modularity of large stylesheets.
** Improved handling of dynamic errors with, for example, an xsl:try instruction.
** Support for maps and arrays, enabling XSLT to handle JSON as well as XML.
** Functions can now be arguments to other (higher-order) functions.

==Design and processing model==
[[Image:XSLT en.svg|right|thumb|Diagram of the basic elements and process flow of eXtensible Stylesheet Language Transformations.]]
The XSLT processor takes one or more XML source documents, plus one or more XSLT stylesheets, and processes them to produce one or multiple output documents.<ref>{{Citation |last1=Flatt |first1=Amelie |title=Phase III: Generating Artifacts from the Model |date=2022 |url=https://link.springer.com/10.1007/978-3-031-14132-4_5 |work=Model-Driven Development of Akoma Ntoso Application Profiles |pages=31–37 |place=Cham |publisher=Springer International Publishing |language=en |doi=10.1007/978-3-031-14132-4_5 |isbn=978-3-031-14131-7 |access-date=2023-01-07 |last2=Langner |first2=Arne |last3=Leps |first3=Olof|url-access=subscription }}</ref><ref>{{Cite web |title=XSL Transformations (XSLT) Version 2.0 (Second Edition) |url=https://www.w3.org/TR/xslt20/#creating-result-trees |access-date=2023-02-07 |website=www.w3.org |quote=Example: Multiple Result Documents}}</ref> In contrast to widely implemented [[imperative programming]] languages like [[C (programming language)|C]], XSLT is [[Declarative programming|declarative]].<ref>{{cite web |title=Discover the Wonders of XSLT: XSLT Quirks |url=http://www.developer.com/xml/article.php/3357231#Coding%20styles |quote=XSLT is a very specialized language with a distinct declarative flavor. |access-date=2011-02-11 |archive-date=2011-07-09 |archive-url=https://web.archive.org/web/20110709015528/http://www.developer.com/xml/article.php/3357231#Coding%20styles |url-status=dead }}</ref> The basic processing paradigm is pattern matching.<ref name=IBM>{{cite web|last=Kay|first=Michael|title=What kind of language is XSLT?|url=https://www.ibm.com/developerworks/library/x-xslt/|publisher=IBM|access-date=13 November 2013}}</ref> Rather than listing an imperative sequence of actions to perform in a stateful environment, template rules only define how to handle a node matching a particular XPath-like pattern, if the processor should happen to encounter one, and the contents of the templates effectively comprise [[functional programming|functional]] [[expression (programming)|expressions]] that directly represent their evaluated form: the result tree, which is the basis of the processor's output.

A typical processor behaves as follows. First, assuming a stylesheet has already been read and prepared, the processor builds a source [[Tree data structure|tree]] from the input XML document. It then processes the source tree's root node, finds the best-matching template for that node in the stylesheet, and evaluates the template's contents. Instructions in each template generally direct the processor to either create nodes in the result tree, or to process more nodes in the source tree in the same way as the root node. Finally the result tree is serialized as XML or HTML text.

==XPath==
{{details|XPath}}
XSLT uses [[XPath]] to identify subsets of the source document tree and perform calculations. XPath also provides a range of [[subroutine|functions]], which XSLT itself further augments.

XSLT 1.0 uses XPath 1.0, while XSLT 2.0 uses XPath 2.0. XSLT 3.0 will work with either XPath 3.0 or 3.1. In the case of 1.0 and 2.0, the XSLT and XPath specifications were published on the same date. With 3.0, however, they were no longer synchronized; XPath 3.0 became a Recommendation in April 2014, followed by XPath 3.1 in February 2017; XSLT 3.0 followed in June 2017.

==XQuery compared==
{{details|XQuery#XQuery and XSLT compared}}
XSLT functionalities overlap with those of [[XQuery]], which was initially conceived as a query language for large collections of XML documents.

The XSLT 2.0 and XQuery 1.0 standards were developed by separate working groups within [[W3C]], working together to ensure a common approach where appropriate. They share the same data model, type system, and function library, and both include [[XPath]] 2.0 as a sublanguage.

The two languages, however, are rooted in different traditions and serve the needs of different communities. XSLT was primarily conceived as a stylesheet language whose primary goal was to render XML for the human reader on screen, on [[the web]] (as a [[web template|web template language]]), or on paper. XQuery was primarily conceived as a [[database query language]] in the tradition of [[SQL]].

Because the two languages originate in different communities, XSLT is stronger in its handling
of narrative documents with more flexible structure, while XQuery is stronger in its data handling, for example when performing relational joins.<ref>{{Cite web |title=Saxonica: XSLT and XQuery |url=https://www.saxonica.com/technology/xslt-and-xquery.xml |access-date=2022-06-29 |website=www.saxonica.com}}</ref>

==Media types==
The <code>&lt;output&gt;</code> element can optionally take the attribute <code>media-type</code>, which allows one to set the [[Internet media type|media type]] (or MIME type) for the resulting output, for example: <code><xsl:output output="xml" media-type="application/xml"/></code>. The XSLT 1.0 recommendation recommends the more general attribute types <code>text/xml</code> and <code>application/xml</code> since for a long time there was no registered media type for XSLT. During this time <code>text/xsl</code> became the de facto standard. In XSLT 1.0 it was not specified how the <code>media-type</code> values should be used.

With the release of the XSLT 2.0, the W3C recommended in 2007 the registration of the MIME media type <code>application/xslt+xml</code><ref>{{cite web|title=XSL Transformations (XSLT) Version 2.0|url=https://www.w3.org/TR/2007/REC-xslt20-20070123/#media-type-registration|publisher=W3C|access-date=19 October 2012}}</ref> and it was later registered with the [[Internet Assigned Numbers Authority]].<ref>{{cite web|title=Application Media Types|url=https://www.iana.org/assignments/media-types/application/index.html|publisher=IANA|access-date=19 October 2012}}</ref>

Pre-1.0 working drafts of XSLT used <code>text/xsl</code> in their embedding examples, and this type was implemented and continued to be promoted by Microsoft in Internet Explorer<ref>{{cite web|title=XSLT Requirements for Viewing XML in a Browser|url=https://msdn.microsoft.com/en-us/library/windows/desktop/ms757857(v=vs.85).aspx|publisher=Microsoft|access-date=19 October 2012}}</ref> and MSXML circa 2012. It is also widely recognized in the <code>xml-stylesheet</code> processing instruction by other browsers. In practice, therefore, users wanting to control transformation in the browser using this processing instruction were obliged to use this unregistered media type.<ref>{{cite book | last=Kay | first=Michael | title=XSLT 2.0 and XPath 2.0 Programmer's Reference | url=https://archive.org/details/xsltxpathprogram00kaym_646 | url-access=limited | year=2008 | publisher=Wiley | isbn=978-0-470-19274-0 | page=[https://archive.org/details/xsltxpathprogram00kaym_646/page/n151 100]}}</ref>

==Examples==
These examples use the following incoming XML document:<syntaxhighlight lang="xml">
<?xml version="1.0" ?>
<persons>
  <person username="JS1">
    <name>John</name>
    <family-name>Smith</family-name>
  </person>
  <person username="MI1">
    <name>Morka</name>
    <family-name>Ismincius</family-name>
  </person>
</persons>
</syntaxhighlight>

===Example 1 (transforming XML to XML)===
This XSLT stylesheet provides templates to transform the XML document:<syntaxhighlight lang="xml">
<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="1.0">
  <xsl:output method="xml" indent="yes"/>

  <xsl:template match="/persons">
    <root>
      <xsl:apply-templates select="person"/>
    </root>
  </xsl:template>

  <xsl:template match="person">
    <name username="{@username}">
      <xsl:value-of select="name" />
    </name>
  </xsl:template>

</xsl:stylesheet>
</syntaxhighlight>

Its evaluation results in a new XML document, having another structure:

<syntaxhighlight lang="xml">
<?xml version="1.0" encoding="UTF-8"?>
<root>
  <name username="JS1">John</name>
  <name username="MI1">Morka</name>
</root>
</syntaxhighlight>

===Example 2 (transforming XML to XHTML)===
Processing the following example XSLT file
<syntaxhighlight lang="xml">
<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet
  version="1.0"
  xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
  xmlns="http://www.w3.org/1999/xhtml">

  <xsl:output method="xml" indent="yes" encoding="UTF-8"/>

  <xsl:template match="/persons">
    <html>
      <head> <title>Testing XML Example</title> </head>
      <body>
        <h1>Persons</h1>
        <ul>
          <xsl:apply-templates select="person">
            <xsl:sort select="family-name" />
          </xsl:apply-templates>
        </ul>
      </body>
    </html>
  </xsl:template>

  <xsl:template match="person">
    <li>
      <xsl:value-of select="family-name"/><xsl:text>, </xsl:text><xsl:value-of select="name"/>
    </li>
  </xsl:template>

</xsl:stylesheet>
</syntaxhighlight>
with the XML input file shown above results in the following [[XHTML]] ([[whitespace (computer science)|whitespace]] has been adjusted here for clarity):
<syntaxhighlight lang="xml">
<?xml version="1.0" encoding="UTF-8"?>
<html xmlns="http://www.w3.org/1999/xhtml">
  <head> <title>Testing XML Example</title> </head>
  <body>
    <h1>Persons</h1>
      <ul>
        <li>Ismincius, Morka</li>
        <li>Smith, John</li>
      </ul>
  </body>
</html>
</syntaxhighlight>
This XHTML generates the output below when rendered in a web browser.
[[Image:xslt ex2.png|thumb|center|Rendered XHTML generated from an XML input file and an XSLT transformation.]]

In order for a web browser to be able to apply an XSL transformation to an XML document on display, an XML stylesheet processing instruction can be inserted into XML. So, for example, if the stylesheet in Example 2 above were available as "example2.xsl", the following instruction could be added to the original incoming XML:<ref name=w3cxslt>{{cite web | url = https://www.w3.org/TR/xslt#section-Embedding-Stylesheets | title = XSL Transformations (XSLT) Version 1.0: W3C Recommendation&nbsp;– Embedding Stylesheets | date = 16 November 1999 | publisher = W3C | access-date = 20 September 2016}}</ref>

<syntaxhighlight lang="xml">
<?xml-stylesheet href="example2.xsl" type="text/xsl" ?>
</syntaxhighlight>

In this example, <code>text/xsl</code> is technically incorrect according to the W3C specifications<ref name=w3cxslt /> (which say the type should be <code>application/xslt+xml</code>), but it is the only media type that is widely supported across browsers as of 2009, and the situation is unchanged in 2021.

==Processor implementations==
*RaptorXML from [[Altova]] is an XSLT 3.0 processor available in the XMLSpy development toolkit and as a free-standing server implementation, invoked using a REST interface.
*[[IBM]] offers XSLT processing embedded in a special-purpose hardware appliance under the [[IBM WebSphere DataPower SOA Appliances|Datapower]] brand.
*[[libxslt]] is a [[free software|free]] [[library (computing)|library]] released under the [[MIT License]] that can be reused in commercial applications. It is based on [[libxml]] and implemented in [[C (programming language)|C]] for speed and portability. It supports XSLT 1.0 and [[EXSLT]] extensions.<ref>{{cite web|title=The XSLT C library for GNOME: libxslt|url=http://xmlsoft.org/XSLT/index.html|access-date=23 November 2012}}</ref>
**It can be used at the command line via xsltproc<ref>{{cite web|title=The XSLT C library for GNOME: The xsltproc tool|url=http://xmlsoft.org/XSLT/xsltproc2.html|access-date=23 November 2012}}</ref> which is included in [[macOS]]<ref>{{cite web|title=xsltproc man page|url=https://developer.apple.com/library/mac/#documentation/Darwin/Reference/ManPages/man1/xsltproc.1.html|access-date=23 November 2012}}</ref> and many [[Linux distributions]], and can be used on [[Microsoft Windows|Windows]] via [[Cygwin]].<ref>{{cite web|title=New package: libxslt|url=https://www.cygwin.com/ml/cygwin-announce/2002/msg00018.html|access-date=23 November 2012}}</ref>
**The [[WebKit]] and [[Blink (layout engine)|Blink]] layout engines, used for example in the [[Apple Safari|Safari]] and [[Google Chrome|Chrome]] web browsers respectively, uses the libxslt library to do XSL transformations.<ref>{{cite web | url=https://webkit.org/projects/xslt/index.html | title=The WebKit Open Source Project – XSLT | access-date=2009-10-25}}</ref>
**[[Language binding|Bindings]] exist for [[Python (programming language)|Python]],<ref>{{cite web|title=The XML C parser and toolkit of Gnome: Python and bindings|url=http://xmlsoft.org/python.html|access-date=23 November 2012}}</ref> [[Perl]],<ref>{{cite web|title=XML::LibXSLT – Interface to the GNOME libxslt library|url=https://metacpan.org/module/XML::LibXSLT|publisher=CPAN|access-date=23 November 2012}}</ref> [[Ruby (programming language)|Ruby]],<ref>{{cite web|title=libxslt-ruby|url=https://rubygems.org/gems/libxslt-ruby|access-date=23 November 2012}}</ref> [[PHP]],<ref>{{cite web|title=libxml|url=https://www.php.net/manual/en/book.libxml.php|access-date=23 November 2012}}</ref> [[Common Lisp]],<ref>{{cite web|title=cl-libxml2 High-level wrapper around libxml2 and libxslt libraries |url=https://code.google.com/p/cl-libxml2/}}</ref> [[Tcl]],<ref>{{cite web|title=TclXML|url=https://tclxml.sourceforge.net/|access-date=21 May 2013}}</ref> and [[C++]].<ref>{{cite web|title=libxml++|url=https://libxmlplusplus.sourceforge.net/|publisher=sourceforge.net|access-date=23 November 2012}}</ref>
*[[Microsoft]] provides two XSLT processors (both XSLT 1.0 only). The earlier processor [[MSXML]] provides COM interfaces; from MSXML 4.0 it also includes the command line utility <code>msxsl.exe</code>.<ref>{{cite web|title=Command Line Transformation Utility (msxsl.exe)|url=http://www.microsoft.com/en-us/download/details.aspx?id=21714|publisher=Microsoft|access-date=22 October 2012}}</ref> The .NET runtime includes a separate built-in XSLT processor in its <code>System.Xml.Xsl</code> library.
*[[Saxon XSLT|Saxon]] is an XSLT 3.0 and XQuery 3.1 processor with [[open-source software|open-source]] and [[proprietary software|proprietary]] versions for stand-alone operation and for [[Java (programming language)|Java]], [[JavaScript]] and .NET. A separate product Saxon-JS<ref>{{cite web|title=Saxon-JS|url=https://www.saxonica.com/saxon-js/index.xml|publisher=Saxonica|access-date=6 September 2018}}</ref> offers XSLT 3.0 processing on [[Node.js]] and in the browser.
*[https://github.com/egh/xjslt xjslt] is an [[open-source software|open-source]] XSLT 2.0 compiler for [[JavaScript]] supporting [[Node.js]] and the browser.
*[[Xalan]] is an open source XSLT 1.0 processor from the [[Apache Software Foundation]] available for Java and C++. A variant of the Xalan processor is included as the default XSLT processor in the standard Java distribution from Oracle.
*Web browsers: Safari, Chrome, Firefox, Opera and Internet Explorer all support XSLT 1.0 (only).<ref>{{cite web |title=Common XSLT Errors |url=https://developer.mozilla.org/en-US/docs/Web/XSLT/Common_errors |website=MDN Web Docs |publisher=Mozilla |access-date=16 September 2024 |date=10 July 2023}}</ref> Browsers can perform on-the-fly transformations of XML files and display the transformation output in the browser window. This is done either by embedding the XSL in the XML document or by referencing a file containing XSL instructions from the XML document. The latter may not work with Chrome on files from local filesystem because of its security model.<ref>{{cite web |url= https://bugs.chromium.org/p/chromium/issues/detail?id=58151 |title=Issue 58151: Fails to load xml file on local file system using XMLHttpRequest }}</ref>
*Adobe AXSLE engine, a proprietary library

===Performance===
Most early XSLT processors were interpreters.  More recently, code generation is increasingly common, using portable intermediate languages (such as [[Java bytecode]] or .NET [[Common Intermediate Language]]) as the target. However, even the interpretive products generally offer separate analysis and execution phases, allowing an optimized expression tree to be created in memory and reused to perform multiple transformations. This gives substantial performance benefits in online publishing applications, where the same transformation is applied many times per second to different source documents.<ref>[http://www-128.ibm.com/developerworks/xml/library/x-xslt2/ Saxon: Anatomy of an XSLT processor] – Article describing implementation &amp; optimization details of a popular XSLT processor.</ref> This separation is reflected in the design of XSLT processing APIs (such as [[Java API for XML Processing|JAXP]]).

Early XSLT processors had very few optimizations.  Stylesheet documents were read into [[Document Object Model]]s and the processor would act on them directly. [[XPath]] engines were also not optimized. Increasingly, however, XSLT processors use optimization techniques found in functional programming languages and database query languages, such as static rewriting of an expression tree (e.g., to move calculations out of loops), and lazy pipelined evaluation to reduce the [[memory footprint]] of intermediate results (and allow "early exit" when the processor can evaluate an expression such as <code>following-sibling::*[1]</code> without a complete evaluation of all subexpressions). Many processors also use tree representations that are significantly more efficient (in both space and time)<ref>{{Cite journal|title=Improving Pattern Matching Performance in XSLT|first1=John|last1=Lumley|first2=Michael|last2=Kay|date=June 2015|journal=XML London 2015|doi=10.14337/XMLLondon15.Lumley01|url=https://xmllondon.com/2015/presentations/lumley|pages=9–25|article-number=1 |doi-broken-date=12 July 2025 |isbn=978-0-9926471-2-4|doi-access=free}}</ref> than general-purpose DOM implementations.

In June 2014, Debbie Lockett and [[Michael Howard Kay|Michael Kay]] introduced an open-source benchmarking framework for XSLT processors called XT-Speedo.<ref>{{Cite journal|title=Benchmarking XSLT Performance|first1=Michael|last1=Kay|first2=Debbie|last2=Lockett|date=June 2014|journal=XML London 2014|doi=10.14337/XMLLondon14.Kay01|url=https://xmllondon.com/2014/presentations/kay|pages=10–23|article-number=1 |doi-broken-date=12 July 2025 |isbn=978-0-9926471-1-7|doi-access=free}}</ref>

==See also==
* [[XSLT elements]] – a list of some commonly used XSLT structures.
* [[XSLT/Muenchian grouping|Muenchian grouping]] – a dialect differential between XSLT1 and XSLT2+.
* [[Extensible Stylesheet Language|eXtensible Stylesheet Language]] – a family of languages of which XSLT is a member
* [[XQuery#XQuery and XSLT compared|XQuery and XSLT compared]]
* [[XSL Formatting Objects|XSL formatting objects]] or ''XSL-FO'' – An XML-based language for documents, usually generated by transforming source documents with XSLT, consisting of objects used to create formatted output
* [[Identity transform]] – a starting point for filter chains that add or remove data elements from XML trees in a transformation pipeline
* [[Apache Cocoon]] – a [[Java (programming language)|Java]]-based framework for processing data with XSLT and other transformers.

==References==
{{Reflist|30em}}

==Further reading==
* ''XSLT'' by Doug Tidwell, published by O’Reilly ({{ISBN|0-596-00053-7}})
* ''XSLT Cookbook'' by Sal Mangano, published by O’Reilly ({{ISBN|0-596-00974-7}})
* ''XSLT 2.0 Programmer's Reference'' by [[Michael Howard Kay|Michael Kay]] ({{ISBN|0-764-56909-0}})
* ''XSLT 2.0 and XPath 2.0 Programmer's Reference'' by Michael Kay ({{ISBN|978-0-470-19274-0}})
* ''XSLT 2.0 Web Development'' by Dmitry Kirsanov ({{ISBN|0-13-140635-3}})
* ''XSL Companion, 2nd Edition'' by Neil Bradley, published by Addison-Wesley ({{ISBN|0-201-77083-0}})
* ''XSLT and XPath on the Edge (Unlimited Edition)'' by [[Jeni Tennison]], published by Hungry Minds Inc, U.S. ({{ISBN|0-7645-4776-3}})
* ''XSLT & XPath, A Guide to XML Transformations'' by John Robert Gardner and Zarella Rendon, published by Prentice-Hall ({{ISBN|0-13-040446-2}})
* ''XSL-FO'' by Dave Pawson, published by O'Reilly ({{ISBN|978-0-596-00355-5}})

==External links==
{{Wikibooks|XML – Managing Data Exchange/XSLT and Style Sheets}}
{{Commons category|Extensible Stylesheet Language Transformations}}
; Documentation
* [https://www.w3.org/TR/xslt-10/ XSLT 1.0 W3C Recommendation]
* [https://www.w3.org/TR/xslt20/ XSLT 2.0 W3C Recommendation]
* [https://www.w3.org/TR/xslt-30/ XSLT 3.0 W3C Recommendation]
* {{cite web |url=https://developer.mozilla.org/en-US/docs/Web/XML/XSLT |title=XSLT: Extensible Stylesheet Language Transformations |website=MDN |access-date=2025-02-09}}
* [https://msdn.microsoft.com/en-us/library/ms256069.aspx XSLT Reference (MSDN)]
* [https://saxon.sourceforge.net/saxon7.5/xsl-elements.html XSLT Elements (Saxon)]
* [https://data2type.de/en/xml-xslt-xslfo/xslt/ XSLT introduction and reference]

; XSLT code libraries
* [https://exslt.github.io EXSLT] is a widespread community initiative to provide extensions to XSLT.
* [https://fxsl.sf.net/ FXSL] is a library implementing support for [[Higher-order function]]s in XSLT. FXSL is written in XSLT itself.
* [https://xsltsl.sourceforge.net/ The XSLT Standard Library] xsltsl, provides the XSLT developer with a set of XSLT templates for commonly used functions. These are implemented purely in XSLT, that is they do not use any extensions. xsltsl is a SourceForge project.
* [https://kernowforsaxon.sf.net/ Kernow] A GUI for Saxon that provides a point and click interface for running transforms.
* [http://johannburkard.de/software/xsltjs/ xslt.js&nbsp;– Transform XML with XSLT] JavaScript library that transforms XML with XSLT in the browser.

{{XSL}}
{{W3C Standards}}

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[[Category:Programming languages created in 1998]]
[[Category:Transformation languages]]
[[Category:World Wide Web Consortium standards]]
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