This interface defines methods that are called by Saxon during the execution of
a stylesheet, if tracing is switched on. Tracing can be switched on by nominating
an implementation of this class using the TRACE_LISTENER feature of the TransformerFactory,
or using the addTraceListener() method of the Controller, which is Saxon's implementation
of the JAXP javax.xml.transform.Transformer interface.
9.7. The TraceListener2 interface extends the TraceListener interface, which
is retained for compatibility.