A description of the extinction-correction method applied. This description should include information about the correction method, either 'Becker-Coppens' or 'Zachariasen'. The latter is sometimes referred to as the 'Larson' method even though it employs Zachariasen's formula. The Becker-Coppens procedure is referred to as 'type 1' when correcting secondary extinction dominated by the mosaic spread; as 'type 2' when secondary extinction is dominated by particle size and includes a primary extinction component; and as 'mixed' when there is a mixture of types 1 and 2. For the Becker-Coppens method, it is also necessary to set the mosaic distribution as either 'Gaussian' or 'Lorentzian' and the nature of the extinction as 'isotropic' or 'anisotropic'. Note that if either the 'mixed' or 'anisotropic' corrections are applied, the multiple coefficients cannot be contained in *_extinction_coef and must be listed in _refine.details. Ref: Becker, P. J. & Coppens, P. (1974). Acta Cryst. A30, 129-147, 148-153. Zachariasen, W. H. (1967). Acta Cryst. 23, 558- 564. Larson, A. C. (1967). Acta Cryst. 23, 664-665.