"The element with local name for-each-group does not exist in XSL-T."

Am I missing something?

I am using Qt 4.8.4.
I am calling QXmlQuery like this:

@
QXmlQuery xmlQuery(QXmlQuery::XSLT20);
xmlQuery.setMessageHandler(&messageHandler);
xmlQuery.setFocus(&xmlBuffer);
xmlQuery.setQuery(&queryFile);
@

The line from my XSL file looks like this:

@
<xsl:for-each-group select="../readings/slot" group-by="@slot_dtm">
@

Thanks.