@Override
    public void startDocument() throws SAXException {
        handler.startDocument();
    }
Receive notification of the beginning of a document.
<p>
<p>
The SAX parser will invoke this method only once, before any other event
callbacks (except for {@link #setDocumentLocator setDocumentLocator}).
</p>

@throws org.xml.sax.SAXException any SAX exception, possibly wrapping another exception
@see #endDocument
stroom-pipeline/src/main/java/stroom/pipeline/filter/ContentHandlerAdaptor.java