docs: def cross(self, vec):
          """Cross product with another Vector3Array"""
          if not isinstance(vec, Vector3Array):
              raise TypeError('Cross product operand must be a Vector3Array')
          if self.nV != 1 and vec.nV != 1 and self.nV != vec.nV:
              raise ValueError('Cross product operands must have the same '
                               'number of elements.')
          return Vector3Array(np.cross(self, vec))