It covers some 35 basic subcategorisation frames and for each of these frames, the set of argument redistributions (active, passive, middle, neuter, reflexivisation, impersonal, passive impersonal) and of argument realisations (cliticisation, extraction, omission, permutations, etc.)
from the NLG geared paradigm, it takes the ability to symbolically constrain the realiser output to a given generation context.