invoke {source : <Sid>, target : <Sid>}
This verifies the permissibility of data streams from the source subject to the target subject.
It returns the "granted" result if the integrity level of the target subject does not exceed the integrity level of the source subject.
It returns the "denied" result in the following cases:
target subject exceeds the integrity level of the source subject.target subject is incomparable to the integrity level of the source subject.source subject or to the target subject.source or target value is outside of the permissible range.