The code identifying the class to which this reflection has been assigned. This code must match a value of _reflns_class.code. Reflections may be grouped into classes for a variety of purposes. For example, for modulated structures each reflection class may be defined by the number m=sum|m_i|, where the m_i are the integer coefficients that, in addition to h,k,l, index the corresponding diffraction vector in the basis defined for the reciprocal lattice.