private String getKeyText(final String key) {
        return LogUtil.message("key [{}]", key);
    }
This method applies a post processing function if we are currently within
a function element. At this stage we should have details of the function
to apply from the corresponding start element and content to apply it to
from the characters event.

@param uri       The element's Namespace URI, or the empty string.
@param localName The element's local name, or the empty string.
@param qName     The element's qualified (prefixed) name, or the empty string.
@throws org.xml.sax.SAXException The client may throw an exception during processing.
@see stroom.pipeline.filter.AbstractXMLFilter#endElement(java.lang.String,
java.lang.String, java.lang.String)
stroom-pipeline/src/main/java/stroom/pipeline/refdata/ReferenceDataFilter.java