The following code:
Results in an exception XPath_TokenNotSupported being thrown from XPathScannerForSchema::addToken. The latest being called in XPathScanner::scanExpression.
The XPathScannerForSchema object is created in XercesXPath::parseExpression.
I don't know if this is an unwanted behavior as the XPath expression is valid according to https://www.w3.org/TR/xpath/#path-abbrev or if the XPath parsing ins't fully implemented and this syntax isn't supported yet (therefore this issue should rather be an improvement request). Anyway this is a bit annoying.