What is the origin of the idiom "back to front" and when to use it?

The origin of the phrase "back to front" is not precisely documented, but it is an idiom used to describe a deep and thorough understanding or knowledge of a subject. It suggests that someone is highly familiar with every aspect, detail, or component of that subject, as if they have explored it completely from one end to the other, much like knowing both the front and back of a book.