@Override
    @Deprecated
    public void printXml(XmlStream xml) {
        XmlSerializationHelper.printStringXml(this, xml);
        //TODO: add spanTree printing
    }
Prints XML in Vespa Document XML format for this StringFieldValue.

@param xml the stream to print to
document/src/main/java/com/yahoo/document/datatypes/StringFieldValue.java