Function yundo_manager_undo 

#[unsafe(no_mangle)]
pub unsafe extern "C" fn yundo_manager_undo(
    mgr: *mut YUndoManager,
) -> u8

Performs an undo operations, reverting all the changes defined by the last undo stack item. These changes can be then reapplied again by calling yundo_manager_redo function.

Returns Y_TRUE if successfully managed to do an undo operation. Returns Y_FALSE if undo stack was empty or if undo couldn’t be performed (because another transaction is in progress).