Stephen Carlson wrote:OK, Some theories of information structure, like Lambrecht's, don't allow topic and focus to overlap. Others like Kirfka's do permit it if the topic is a contrastive topic. I can readily see that Κίσσοι in Hdt 7.62.2 is a contrastive topic (cf. the Μῆδοι in Hdt 7.62.1), but I can't really see that for Matt 2:1. I can't remember Dik's position on this this, however.
I don't know if Lambrecht would necessarily disallow it, since for him, focus isn't defined by the newness of the information, but by whether or not the information is being asserted. At the same time, the idea of new information being associated with a topic probably wouldn't be accepted. So, I suppose he would say that focus may or may not be new information, but topic cannot be new information. Anyway...
Nick Bailey's discussion of ἰδοὺ deals with this construction: ἰδού + subject-phrase + finite-verb starting on page 339 of his dissertation. He argues that the construction mimics other thetic uses of ἰδού, but cannot be viewed as a predicator since the construction involves a finite verb. At the same time, it still is thetic/presentational,and thus, the pre-verbal subject is focal/asserted. In some instances, ἰδού is activating a participant that is known, but not directly accessible in the audience's mental representation (e.g. Matthew 12:46).