code: def save(self, outfname):
          
          f = BZ2File(outfname, 'w')
          self.doc.writexml(f, addindent='  ', newl='\n')
          f.close()
docs: Save the environment of a sv file to be used with soniv visualiser
          
          Args:
            outfname(str): full path to the file storing the environment