-struct categoricals *categoricals_create (struct interaction *const *, size_t n_int,
- const struct variable *wv, enum mv_class dep_excl,
- enum mv_class fctr_excl);
+/* Categoricals.
+
+ A categorical variable has a finite and usually small number of possible
+ values. The categoricals data structure organizes an array of interactions
+ maong categorical variables, that is, a set of sets of categorical
+ variables. (Both levels of "set" are ordered.)
+
+ The life cycle of a categoricals object looks like this:
+
+ 1. Create it with categoricals_create(). This fixes the set of interactions
+ and other parameters.
+
+ 2. Pass all of the desired cases through the object with
+ categoricals_update().
+
+ 3. Finalize the object with categoricals_done(). Only at this point may
+ most of the categoricals query functions be called.
+
+ 4. Use the categoricals object as desired.
+
+ 5. Destroy the object with categoricals_destroy().
+*/