I noticed there is a new transaction option when you right-click a transaction: "Add Reversing." I couldn't find it in the documentation. What does this option do?

I've never used it, but I believe it adds a new transaction identical to the one you right clicked on but reversing the sign of every split. It can be useful if a transaction was entered in error, but you have already reconciled, so simply deleting the old one would be harder to deal with. I would have to check the git log to see when it was added and whether there was a particular reason or bug it was in response to.

Here's the corresponding commit.