Customizing Assert Error Messages
To customize the error messages that the Xerces or Saxon validation engines display
            for the
            assert and assertion elements, set the
            message attribute on these elements.
            
- For Xerces, the messageattribute has to belong to thehttp://xerces.apache.orgnamespace.
- For Saxon, the messageattribute has to belong to thehttp://saxon.sourceforge.net/namespace.
message attribute is the error message displayed if
            the assertion fails.
         
      