Adding support for assertions

[vbence]

It would be nice to handle inter-field validation with XML Scehma's assert mechanism.
http://www.w3.org/TR/xmlschema11-1/#cAssertions

As JAXB is a given, running XPath expressions on the marshalled representation should be straightforward.

[whummer]

Sounds like a useful extension, will look into this...

[vbence]

As a first step it would be nice just to include this information in schema generation. Actual validation could even be a different milestone.

[whummer]

Added support for assertions in version 1.2.0. Note that this currently only works if using JAXB directly, integration with JAX-WS (including wsimport) is not possible because XML Schema 1.1 features don't seem to be supported there.

To disable the feature you can set the XmlSchemaEnhancer.XSD_11_ENABLED flag to false.

Currently there is only a very limited set of test cases for this feature, please feel free to provide more tests for different corner cases.