This code system http://hl7.org/fhir/assert-operator-codes defines the following codes:
| Code | Display | Definition |
| equals | equals | Default value. Equals comparison. |
| notEquals | notEquals | Not equals comparison. |
| in | in | Compare value within a known set of values. |
| notIn | notIn | Compare value not within a known set of values. |
| greaterThan | greaterThan | Compare value to be greater than a known value. |
| lessThan | lessThan | Compare value to be less than a known value. |
| empty | empty | Compare value is empty. |
| notEmpty | notEmpty | Compare value is not empty. |
| contains | contains | Compare value string contains a known value. |
| notContains | notContains | Compare value string does not contain a known value. |
| eval | evaluate | Evaluate the fluentpath expression as a boolean condition. |