Extensible Stylesheet Language

XSL, acronym for eXtensible Stylesheet Language, is a family of languages developed by the World Wide Web Consortium (W3C) that allow describing how the information contained in an XML document should be presented.

This language consists of three W3C recommendations:

• XSL Transformations (XSLT): allows you to transform XML documents from one syntax to another.
• XSL Formatting Objects (XSL-FO): specifies the visual format with which the document is intended.
• XML Path Language (XPath): allows you to search and access the document nodes, as well as select parts of the document.

History

XSL began as a proposal by Microsoft, Inso and Arbortext to the W3C in 1997. The SGML language, from which XML was created, already had its own standard for representing its documents, the Document Style Semantics and Specification Language (DSSSL). Therefore, the idea was to create a language based on it for the transformation and representation of XML documents.

XSL development began in January 1998 with the formation of the W3C Working Group for XSL. Throughout the year 1999 XSLT and XPath were developed and XSL-FO a year later. XSLT and XPath became W3C Recommendations in 1999, while XSL-FO gained it in 2001.

XSL languages

XSL Transformations

XSL Transformations (XSLT) presents a way to transform XML documents into other and even non-XML formats (such as HTML).

This transformation is performed using one or more template rules. These template rules attached to the source document to be transformed feed an XSLT processor, which performs the desired transformations by putting the result in an output file, or as in the case of a web page, directly on a display device, as the user monitor.

XSL Path Language

XML Path Language (XPath) is a language that allows you to build expressions that traverse and process an XML document. The idea is similar to regular expressions for selecting parts of plain text (plain text). XPath allows you to search and select taking into account the hierarchical structure of the XML.

XPath was created for use in the XSLT standard, where it is used to select and examine the structure of the transformation input document. To do this, an XML document is processed by a parser (or parser ), building a tree of nodes. This tree starts with a root element, which branches out through the elements that hang from it and ends in leaf nodes, which contain only text, comments, processing instructions or even that are empty and only have attributes.

XSL Formatting Objects

XSL Formatting Objects (XSL-FO) is a language that specifies how data in an XML document is to be formatted for presentation on the screen, on paper, or in other media. It should be noted that the XSL-FO document contains both the data and the format that will be applied to them.

The basic unit of work in an XSL-FO document is the "Formating Object", the basic unit for presenting (formatting) the information. These formatting objects refer to pages, paragraphs, tables, etc.