private String formatIdentifyingVisitorErrorString(String details) {
        return String.format(
                    "Visitor %s (selection '%s'): %s",
                    sessionName,
                    params.getDocumentSelection(),
                    details);
    }
Called from the constructor to ensure control and data handlers
are set and initialized.
documentapi/src/main/java/com/yahoo/documentapi/messagebus/MessageBusVisitorSession.java