checkCIF procedure

PLAT109

 The SHELXL TWIN instruction matrix corresponds to an inverted 
 non-centrosymmetric pointgroup operation belonging to the corresponding 
 centrosymmetric Laue group. The reported twinning factor is actually the
 Flack x value. The close to zero CIF reported Flack parameter value is 
 meaningless.  Please re-refine with the TWIN instruction replaced by 'TWIN'
 (i.e. without numerical data).