XQuery 1.0 implementation

A new configuration option has been added for XQuery processing: FeatureKeys.XQUERY_MULTIPLE_MODULE_IMPORTS. The option is false by default, and should be set to true to retain the behaviour of previous releases. If the option is false, then when an import module declaration is encountered for a particular module namespace URI, and there is already a loaded module for that namespace, then the existing module is used without checking whether the module location URI matches. If the option is true, then the existing module is used only if the location URI matches.