code: def set_section_order(self, section_name_list):
          
          self.section_headings = section_name_list[:]
          for section_name in self.sections.keys():
              if section_name not in section_name_list:
                  self.section_headings.append(section_name)
          return
docs: Set the order of the sections, which are by default unorderd.
  
          Any unlisted sections that exist will be placed at the end of the
          document in no particular order.