The type style-warning includes those conditions that represent situations involving code that is conforming code but that is nevertheless considered to be faulty or substandard.
An implementation might signal such a condition if it encounters code that uses deprecated features or that appears unaesthetic or inefficient.
An ‘unused variable’ warning must be of type style-warning.
In general, the question of whether code is faulty or substandard is a subjective decision to be made by the facility processing that code. The intent is that whenever such a facility wishes to complain about code on such subjective grounds, it should use this condition type so that any clients who wish to redirect or muffle superfluous warnings can do so without risking that they will be redirecting or muffling other, more serious warnings.