@PipelineProperty(
            description = "The depth of XML elements to merge at.",
            defaultValue = "1",
            displayPriority = 1)
    public void setMergeDepth(final int mergeDepth) {
        // Add a fudge in here to cope with legacy depth being 0 based.
        this.mergeDepth = mergeDepth;
    }
@param ch     the characters from the XML document
@param start  the start position in the array
@param length the number of characters to read from the array
@throws org.xml.sax.SAXException any SAX exception, possibly wrapping another exception
@see #characters
@see stroom.pipeline.filter.AbstractXMLFilter#ignorableWhitespace(char[],
int, int)
stroom-pipeline/src/main/java/stroom/pipeline/filter/MergeFilter.java