Function redo 

pub fn redo(
    doc: &mut AutoCommit,
    scope: &Scope,
    limit: usize,
    restore: impl FnMut(&Version) -> Result<Option<Box<dyn Action>>, String>,
) -> Result<Vec<Version>, String>

Bring back the last limit undos of scope, as one new change: an outside step through the action restore gives for it (its recorded action, run again), any other by reverting the undo. A positive pending marker keeps such a step undone until its restoration settles. Returns the undo changes it brought back, newest first.

Errors

Says why nothing was redone: no undo of the scope’s is in effect, a newer step of its own came after it, or a restoration cannot be applied.