If the value constraint check fails (during import or when setting a property), the JCR specification stipulates that a repository throw a javax.jcr.nodetype.ConstraintViolationException. But when importing an XML file with a value that does violate the constraint of a property definition, this exception is actually wrapped by org.modeshape.jcr.JcrContentHandler.EnclosingSAXException (which is a checked one) and the client hast to extract the real cause explicitly.