docs: def max_variants(composition):
      """Calculates the maximum number of isotopic variants that could be produced by a
      composition.
  
      Parameters
      ----------
      composition : Mapping
          Any Mapping type where keys are element symbols and values are integers
  
      Returns
      -------
          max_n_variants : int
      """
      max_n_variants = 0
  
      for element, count in composition.items():
          if element == "H+":
              continue
          try:
              max_n_variants += count * periodic_table[element].max_neutron_shift()
          except KeyError:
              pass
  
      return max_n_variants