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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def fold(self):
 """Folds the region."""

        start, end = self.get_range()
        TextBlockHelper.set_collapsed(self._trigger, True)
        block = self._trigger.next()
        while block.blockNumber() <= end and block.isValid():
            block.setVisible(False)
            block = block.next()