code: def add(self, order, cells, no_validation=False):
          
  
          self._normalized = False
  
          order = self._validate_order(order)
  
          if no_validation:
              # Simply add the given cells to the set with no validation.
              self._orders[order].update(cells)
  
          else:
              # Collect validated cell numbers in a set for addition.
              cell_set = set()
  
              for cell in cells:
                  cell = self._validate_cell(order, cell)
                  cell_set.add(cell)
  
              self._orders[order].update(cell_set)
docs: Add cells at a given order to the MOC.
  
          The cells are inserted into the MOC at the specified order.  This
          leaves the MOC in an un-normalized state.  The cells are given
          as a collection of integers (or types which can be converted
          to integers).
  
          >>> m = MOC()
          >>> m.add(4, (20, 21))
          >>> m.cells
          2
  
          >>> m.add(5, (88, 89))
          >>> m.cells
          4
  
          The `no_validation` option can be given to skip validation of the
          cell numbers.  They must already be integers in the correct range.