docs: def toLily(self):
          '''
          Method which converts the object instance, its attributes and children to a string of lilypond code
  
          :return: str of lilypond code
          '''
          lilystring = "\\version \"2.18.2\" \n"
  
          partstrings = []
          ids_loaded = []
          groupings = []
          if len(self.groups) > 0:
              # here we need to do some set union theory
              lstring, groupings, ids_loaded = self.handleGroups()
              lilystring += lstring
          children = [
              child for child in self.GetSortedChildren() if child not in ids_loaded]
          for child in children:
              part = self.getPart(child)
              partstring = part.toLily()
              lilystring += partstring[0]
              partstrings.append(partstring[1])
          lilystring += self.item.toLily()
          lilystring += "<<"
          lilystring += "".join([gstring for gstring in groupings])
          lilystring += "".join([partstring for partstring in partstrings])
          lilystring += ">>"
          return lilystring