code: def new(self, sort, properties=None):
          
          if sort is None:
              sort = UNKNOWNSORT
          # find next available vid
          vid, index = self.vid, self.index
          while vid in index:
              vid += 1
          varstring = '{}{}'.format(sort, vid)
          index[vid] = varstring
          if properties is None:
              properties = []
          self.store[varstring] = properties
          self.vid = vid + 1
          return (varstring, properties)
docs: Create a new variable for the given *sort*.