首先它是一个Java的开源类库，
它是一个XSLT的处理包，用于将XML文档转为HTML文档，文本文件TXT，或其他格式的XML文档。它实现了XSLT1.0和XPath1.0的接口，可以在命令行调用，或者在applet,servlet中调用，或者作为其他程序的一个模块。
Xalan-Java is an XSLT processor for transforming XML documents into HTML, text, or other XML document types. It implements XSL Transformations (XSLT) Version 1.0 and XML Path Language (XPath) Version 1.0 and can be used from the command line, in an applet or a servlet, or as a module in other program.
Xalan-Java implements the javax.xml.transform interface in Java API for XML Processing (JAXP) 1.3. This interface provides a modular framework and a standard API for performing XML transformations, and utilizes system properties to determine which Transformer and which XML parser to use.
Xalan-Java also implements the javax.xml.xpath interface in JAXP 1.3, which provides an object-model neutral API for evaluation of XPath expressions and access to the evaluation environment.
Xalan-Java also builds on SAX 2 and DOM level 3.