code: def line_up_with_epoch(self):
          
          if self.parent.notes.annot is None:  # TODO: remove if buttons are disabled
              error_dialog = QErrorMessage()
              error_dialog.setWindowTitle('Error moving to epoch')
              error_dialog.showMessage('No score file loaded')
              error_dialog.exec()
              return
  
          new_window_start = self.parent.notes.annot.get_epoch_start(
              self.parent.value('window_start'))
  
          self.parent.overview.update_position(new_window_start)
docs: Go to the start of the present epoch.