The Xalan and Saxon processors support the use of extension elements and extension functions. Unlike a literal result element, which the stylesheet simply transfers to the result tree, an extension element performs an action. The extension is usually used because the XSLT stylesheet fails in providing adequate functions for accomplishing a more complex task.
The DocBook extensions for Xalan and Saxon are included in the [OXYGEN_DIR]\frameworks\docbook\xsl\extensions folder.
For more information about how to use extensions, see the following links: