docs: def clone(self):
          """Return a new bitfield with the same value.
          
          The returned value is a copy, and so is no longer linked to the
          original bitfield.  This is important when the original is located
          at anything other than normal memory, with accesses to it either
          slow or having side effects.  Creating a clone, and working
          against that clone, means that only one read will occur.
          
          """
          temp = self.__class__()
          temp.base = self.base
          return temp