Returns the data for timestamping.
Possible canonicalization methods:
Call this method to get the data which should be used in hash computations for time-stamping.
The data is calculated in the following way: if
URIData is assigned, the result will be simply its value.
Otherwise, if the
URIReference is set, the data is obtained from the referenced place.
If the retrieved data is a ds:Reference element and ReferencedData is True, the data will be processed according to the XMLDSIG processing model. If ReferencedData is False, the result will be a ds:Reference element itself.
If the resulting data is an XML nodeset (or URINode is assigned), the data is canonicalized using CanonicalizationMethod.