docs: def _linefeed(self):
          """
          Performs a line feed.
          """
          last_line = self._cursor.blockNumber() == self._text_edit.blockCount() - 1
          if self._cursor.atEnd() or last_line:
              if last_line:
                  self._cursor.movePosition(self._cursor.EndOfBlock)
              self._cursor.insertText('\n')
          else:
              self._cursor.movePosition(self._cursor.Down)
              self._cursor.movePosition(self._cursor.StartOfBlock)
          self._text_edit.setTextCursor(self._cursor)