code: def collapse_all(self):
          
          self._clear_block_deco()
          block = self.editor.document().firstBlock()
          last = self.editor.document().lastBlock()
          while block.isValid():
              lvl = TextBlockHelper.get_fold_lvl(block)
              trigger = TextBlockHelper.is_fold_trigger(block)
              if trigger:
                  if lvl == 0:
                      self._show_previous_blank_lines(block)
                  TextBlockHelper.set_collapsed(block, True)
              block.setVisible(lvl == 0)
              if block == last and block.text().strip() == '':
                  block.setVisible(True)
                  self._show_previous_blank_lines(block)
              block = block.next()
          self._refresh_editor_and_scrollbars()
          tc = self.editor.textCursor()
          tc.movePosition(tc.Start)
          self.editor.setTextCursor(tc)
          self.collapse_all_triggered.emit()
docs: Collapses all triggers and makes all blocks with fold level > 0
          invisible.