Classification and use of symmetry data

The symmetry CIF dictionary (symCIF) is a small dictionary of data items that refine and extend the definition of symmetry beyond the pragmatic requirements of the core CIF dictionary. The aims are to reflect the current state of space-group theory and to provide rigorous definitions suitable for use in future applications such as software representations of the symmetry properties of space groups, and inclusion of higher-dimensional symmetry in CIFs reporting quasicrystal, magnetic and modulated structures. This chapter is also available as HTML from the International Tables Online site hosted by the IUCr.