Xalan

Xalan is an open-source XSLT processor that is part of the Apache Software Foundation's XML project. It provides two main implementations: Xalan-J, a Java-based library, and Xalan-C++, a C++ library. Both implement the XSLT 1.0 specification and support XPath 1.0, enabling transformation of XML documents into HTML, XML, or plain text. The libraries are designed to work with standard XML parsers such as Xerces and can be used directly or through common APIs like JAXP in Java.

Xalan originated from IBM's XSLT engine and was contributed to the Apache Software Foundation in the late 1990s, where it was developed as part of the XML project. The project is released under the Apache License, providing permissive, open-source access for both commercial and noncommercial use.

In Java environments, Xalan-J is commonly used via JAXP or as a standalone transformer; Xalan-C++ serves similar purposes in C++ applications. The engines support extension functions, templates, and output generation, and they rely on standard interfaces such as DOM and SAX for XML parsing and event handling.

Xalan does not implement newer XSLT versions (such as 2.0 or 3.0); for those features, other processors such as Saxon are typically used. While still available and historically widespread, Xalan’s development activity has slowed in favor of more modern engines.