The values were restricted to non-negative integers since a numeric identifier
values is used when constructing various symmform data item values
(see `_atom_site_moment_Fourier_param.cos_symmform`, 4th component).

The definition range of 0: was taken from the definition of the linked
`_atom_site_Fourier_wave_vector.seq_id` data item from the Modulation
dictionary, however, restricting the range to only positive integers might
also make sense.

…r-seq-id-to-int

…r-seq-id-to-int

…r-seq-id-to-int