Saxon

Fixed by catching an UncheckedXPathException thrown by a Gizmo command, and handling it the same way as a checked XPath exception.

There's a remaining separate issue of duplication in the parser error message:

Error on line 15 column 8 of items.xml:
  SXXP0003   Error reported by XML parser: The markup in the document following the root
  element must be well-formed.: The markup in the document following the root element must
  be well-formed.

The longstanding problem of duplication in the error message appears to happen when we wrap the SAXException thrown by the XML parser in an XPathException. We inherit this code from the parent class TransformerException so there's not much we can do about it.

However, we have already reported the errors quite properly formatted based on the information supplied by the XML parser to the ErrorHandler callback:

Error on line 15 column 8 of items.xml:
  SXXP0003   Error reported by XML parser: The markup in the document following the root
  element must be well-formed.

Perhaps we should recover this information on return from the parser and ignore the actual SAXException that is thrown.