              The code identifying each value of _diffrn_radiation_wavelength.\
               Items in the DIFFRN_RADIATION_WAVELENGTH category are looped \
               when multiple wavelengths are used. \
\
               This code is used to link with the DIFFRN_REFLN category.\
               The _diffrn_refln.wavelength_id codes must match one of \
               the codes defined in this category.