Thank you; these answers have been most insightful! I learned quite a lot from browsing the links. I am writing "answers", plural, because although I post this

Thank you; these answers have been most insightful! I learned quite a lot from browsing the links. I am writing "answers", plural, because although I post this as an answer to SkyMarshals text, I also mean the replies by aban, peller, and petilon.