code: def cursor_down(self, count=1):
          
          original_column = self.preferred_column or self.document.cursor_position_col
          self.cursor_position += self.document.get_cursor_down_position(
              count=count, preferred_column=original_column)
  
          # Remember the original column for the next up/down movement.
          self.preferred_column = original_column
docs: (for multiline edit). Move cursor to the next line.