docs: def _add_fold_decoration(self, block, region):
          """
          Add fold decorations (boxes arround a folded block in the editor
          widget).
          """
          deco = TextDecoration(block)
          deco.signals.clicked.connect(self._on_fold_deco_clicked)
          deco.tooltip = region.text(max_lines=25)
          deco.draw_order = 1
          deco.block = block
          deco.select_line()
          deco.set_outline(drift_color(
              self._get_scope_highlight_color(), 110))
          deco.set_background(self._get_scope_highlight_color())
          deco.set_foreground(QtGui.QColor('#808080'))
          self._block_decos.append(deco)
          self.editor.decorations.append(deco)