[NiLuJe]

We don't give a rat's tail about anything that might be extra in the OPF. The Calibre plugin deals about Calibre metadata, as @pazos said.

(Calibre itself might pick some of it at *import* time, but you'd see those in its tag editor UI).

@Jon: please stop confusing users by talking about things you have no personal experience with, it's becoming *extremely* tiresome, and verging on actively bothersome and generally counter-productive. (And it's not like you haven't been countlessly warned about that very fact...).