Not the poster. What exactly are you asking about?

The usage of the error type the OP wrote is to get the line number of any error without using a macro on top of every single function in our crate.

The person who wrote `MyError` accomplished it by defining their error type as "something that can be constructed from any other error" (`impl From<E: StdErr> for MyError`) and additionally heap-allocated the original error with `Box::new(error)`.

So the usage would be to write one single error type in a crate which can "capture" or be constructed from any error type `E` and also prints out the line number of that error via `impl Display for MyError`.