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There are many changes in Saxon 9.8. These changes, together with a full history of changes in previous releases are comprehensively listed in the Change History.
Saxon 9.8 includes highly conformant implementations of the current W3C Recommendations: XSLT 3.0, XQuery 3.1, XPath 3.1, and XSD 1.1. See Standards Conformance for more details.
Support for older specifications such as XSLT 2.0 and XQuery 1.0 has been dropped, but of course the newer specifications have a high level of backwards compatibility so existing code should continue to run without any problems. Support for two superseded specifications is retained for the time being: XSD 1.0 and XPath 2.0.
XSLT 2.0 and 3.0 define a "backwards compatibility mode" for running XSLT 1.0 stylesheets. From 22.214.171.124 this is reinstated in Saxon-HE, while in earlier versions of 9.8 this is available in Saxon-PE and Saxon-EE only.
This documentation covers three Saxon editions: home, professional, and enterprise (HE, PE, and EE). The Home Edition remains open source (under the Mozilla Public License 2.0). An outline of what is present in each edition can be found in the feature matrix. Broadly speaking, Saxon-HE includes support for published W3C recommendations at the minimum conformance level; Saxon-PE includes support for optional W3C features and for Saxon extensions, and Saxon-EE includes features needed for advanced applications and high performance. See also Choosing a software package.
This documentation covers Saxon on both the Java and .NET platforms. Much of it is also applicable to the Saxon/C product, but you should check the Saxon/C documentation for aspects specific to that platform. The same applies to Saxon-JS.
A full change log is provided.