Halliday & Matthiessen (1999: 529-30):
This focal point usually comes at the end; but (unlike the Theme + Rheme) the Given + New structure is not signalled, in English, by word order — it is signalled by intonation, and specifically by pitch prominence, the point of maximum perturbation (falling, rising or complex) in the intonation contour. The principle behind this is clear: if the Theme always came first, and the New always came last, there would be no possibility of combining them; whereas one powerful form of message — powerful because highly marked — is that in which the two are mapped onto one another, as in no wonder they were annoyed (where the focus is on the interpersonal Theme no wonder.