This code system http://hl7.org/fhir/resource-validation-mode defines the following codes:

CodeDisplayDefinition
createValidate for CreateThe server checks the content, and then checks that the content would be acceptable as a create (e.g. that the content would not violate any uniqueness constraints).
updateValidate for UpdateThe server checks the content, and then checks that it would accept it as an update against the nominated specific resource (e.g. that there are no changes to immutable fields the server does not allow to change, and checking version integrity if appropriate).
deleteValidate for DeleteThe server ignores the content, and checks that the nominated resource is allowed to be deleted (e.g. checking referential integrity rules).