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

            if (definition.Pattern != null)
            {
                IElementNavigator patternValueNav = new PocoNavigator(definition.Pattern);

                if (!instance.Matches(patternValueNav))
                {
                    v.Trace(outcome, $"Value does not match pattern '{toReadable(definition.Pattern)}'",
                            Issue.CONTENT_DOES_NOT_MATCH_PATTERN_VALUE, instance);
                }
            }

            return(outcome);
        }