Unfolds the region.

def unfold(self):
        """Unfolds the region."""
        # set all direct child blocks which are not triggers to be visible
        self._trigger.setVisible(True)
        TextBlockHelper.set_collapsed(self._trigger, False)
        for block in self.blocks(ignore_blank_lines=False):
            block.setVisible(True)
            if TextBlockHelper.is_fold_trigger(block):
                TextBlockHelper.set_collapsed(block, False)