Function undo_since 

pub fn undo_since(
    doc: &mut AutoCommit,
    scope: &Scope,
    heads: &[ChangeHash],
    compensate: impl FnMut(&Version) -> Result<Option<Box<dyn Action>>, String>,
    words: &dyn HistoryWords,
) -> Result<Vec<Version>, String>

Take back every step of scope’s in effect made after the version heads, as one new change: back to a checkpoint or a change from history without counting steps. Returns the steps, newest first.

Errors

As undo.