@Override
    public void startPrefixMapping(final String prefix, final String uri) throws SAXException {
        if (!buffer) {
            super.startPrefixMapping(prefix, uri);
        } else if (inRoot || afterRoot == -1) {
            ensureArraySize();
            events[length++] = new StartPrefixMapping(prefix, uri);
        }
    }
Fired when a prefix mapping is in scope.

@param prefix The prefix.
@param uri    The URI of the prefix.
@throws SAXException Not thrown.
@see stroom.pipeline.filter.AbstractXMLFilter#startPrefixMapping(java.lang.String,
java.lang.String)
stroom-pipeline/src/main/java/stroom/pipeline/filter/SplitFilter.java