Allowed only when the operator values are equal. If not, this MUST result in a policy error.
If a Superior has specified essential=true, then a Subordinate MUST NOT change that. If a Superior has specified essential=false, then a Subordinate is allowed to change that to essential=true. If a Superior has not specified essential, then a Subordinate can set essential to true or false. If those conditions are not met, this MUST result in a policy error.
The result of merging the values of two these operators is the union of the operator values.
The result of merging the values of two these operators is the intersection of the operator values. If the intersection is empty, this MUST result in a policy error.