Halliday & Matthiessen (2014: 279):
For the present discussion, we shall take it that the Identifier always carries the tonic prominence. This is not, in fact, true; it is the typical pattern, since it is the identity that is likely to be new information, but there is a marked option whereby the Identified is construed as the New. (Note therefore that Identified–Identifier cannot simply be explained as Given–New in an ‘identifying’ clause [as Fawcett maintains]; not surprisingly, since the former are experiential functions whereas the latter are textual.)