This is one of those times I wish I could be more specific about things.

I'm looking at a job advertisement, and trying to decide if I should apply. It's calling for something slightly outside my "real" area, but it seems to be a sister school to one I teach at, here. This means that I know exactly what they're looking for and how little of the actual teaching would be in that area.

Meaning, if I were to get the job, I would probably have one course a year that was in this "iffy" area. If I had time to prepare for "iffy" course, it would be relatively easy for me... I've just never taught it before (although I've taught higher-level, more specialized courses in the same area). I don't exactly want to sell myself as a scholar in "iffy" area, but can I teach in it? Sure.

Add to this, the secondary speciality they want is my area.

I guess I apply, discuss both areas equally, and let them decide.