Stage 1 is relatively straight-forward, and is carried out by the option CIF SYNTAX. It is essential that the CIF conforms to the syntactic rules before proceeding to Stage 2.
Stage 2 is more problematical, and is still undergoing fine-tuning. There are two options in WinGX for data-validation under the menu item CIF VALIDATE, i.e. IUCr which checks whether the CIF conforms to the DVN standards required for publication in Acta Cryst C, and PLATON which performs a number of other checks.
It is strongly recommended that BOTH Stage 2 checks are carried out, since they are complementary. Each program indicates potential problems, and their level of severity.