While extremely powerful, XSL has many shortcomings when used to perform system level scripting tasks. Operations such as working with files and advanced string operations are not included in the standard XSL language.

XSL does provide a generic extension mechanism to add new features to the base language. ePublisher Designer provides a standard set of extension objects which enable XSL to generate all required formats.

XSL extensions live in a specific namespace. Users can define their own prefix to associate with a given namespace, but in general sticking with a consistent naming convention makes life easier.