Extends mirt's SingleGroupClass directly (meaning all mirt methods that
work with that class will work with BlisClass too; make sure mirt is
loaded).
orig_levelslist of original levels with logical attribute key,
which stores the information on which response (level) has been considered
as correct. Note that levels not used in the original data are dropped.
The purpose of the class is to have a custom coef method (see
coef,BlisClass-method) dispatched and the original levels with correct
response (as a key attribute) stored in the resulting fitted model.
Other BLIS/BLIRT related:
coef,BlisClass-method,
fit_blis(),
get_orig_levels(),
nominal_to_int(),
obtain_nrm_def(),
print.blis_coefs()