There are numerous theoretical approaches describing IS and its semantics (Halliday, 1967;Sgall, 1967;Vallduví, 1990;Steedman, 2000) and the terminology used is diversesee (Kruijff-Korbayová and Steedman, 2003) for an overview.
applying these rules for the sentence (b) in example (1) we find the Topic and the Focus of the sentence: It is worth mentioning that although most of the time, CB items belong to the Topic and NB items belong to the Focus (as it happens in our example too), there may be cases when the Focus contains some NB items and/or the Topic contains some CB items.