public static OperationOutcome ValidateFixed(this Validator v, ElementDefinition definition, IElementNavigator instance)
        {
            var outcome = new OperationOutcome();

            if (definition.Fixed != null)
            {
                IElementNavigator fixedValueNav = new PocoNavigator(definition.Fixed);

                if (!instance.IsExactlyEqualTo(fixedValueNav))
                {
                    v.Trace(outcome, $"Value is not exactly equal to fixed value '{toReadable(definition.Fixed)}'",
                            Issue.CONTENT_DOES_NOT_MATCH_FIXED_VALUE, instance);
                }
            }

            return(outcome);
        }