The Extensible Stylesheet Language, XSL, defines a set of elements (called formatting objects) that describe how data should be formatted. For clarity, this standard is often referred to as XSL-FO to distinguish it from XSLT. Although it's primarily designed for generating high-quality printable documents, you can also use formatting objects to generate audio files from XML. The XSL-FO standard is at w3.org/TR/xsl/.

The Extensible Stylesheet Language for Transformations, XSLT, is an XML vocabulary that describes how to convert an XML document into something else. The standard is at w3.org/TR/xslt (no closing slash).

XPath, the XML Path Language, is a syntax that describes locations in XML documents. You use XPath in XSLT style sheets to describe which portion of an XML document you want to transform. XPath is used in other XML standards as well, which is why it is a separate standard from XSLT. XPath is defined at w3.org/TR/xpath (no closing slash).