Struct UndoStep 

pub struct UndoStep {
    pub what: String,
    pub marks: Vec<MsgMark>,
    pub sel: Option<PathBuf>,
    pub created: Vec<PathBuf>,
    pub note: Option<String>,
    pub rewritten: Vec<(PathBuf, Vec<u8>)>,
}

One undoable step: what it was, the messages as they stood before it, and where the cursor was.

Fields

what: String

marks: Vec<MsgMark>

sel: Option<PathBuf>

The message the cursor was on, by path: a resort or a limit can move it, so the position alone would not find it again.

created: Vec<PathBuf>

Files the step created (a save or copy’s delivered message), removed again when it is undone.

note: Option<String>

Something the undo cannot take back, said out loud when it runs (a copy that went to an IMAP folder).

rewritten: Vec<(PathBuf, Vec<u8>)>

Messages the step rewrote on disk (break-thread, link-threads), with the bytes they held before, put back when it is undone.