/// <summary>
        /// Validates this Prescription Item
        /// </summary>
        /// <param name="path">The path to this object as a string</param>
        /// <param name="messages">the validation messages to date, these may be added to within this method</param>
        public void Validate(string path, List <ValidationMessage> messages)
        {
            var vb = new ValidationBuilder(path, messages);

            if (vb.ArgumentRequiredCheck("DateTimePrescriptionExpires", DateTimePrescriptionExpires))
            {
                if (DateTimePrescriptionExpires.PrecisionIndicator == null || DateTimePrescriptionExpires.PrecisionIndicator.Value != ISO8601DateTime.Precision.Day || DateTimePrescriptionExpires.TimeZone != null)
                {
                    vb.AddValidationMessage(vb.PathName, null, "SHALL include a complete date (century, year, month and day)");
                }
            }

            vb.ArgumentRequiredCheck("PrescriptionItemIdentifier", PrescriptionItemIdentifier);

            vb.ArgumentRequiredCheck("Directions", Directions);

            if (vb.ArgumentRequiredCheck("TherapeuticGoodIdentification", TherapeuticGoodIdentification))
            {
                TherapeuticGoodIdentification.Validate(vb.Path + "TherapeuticGoodIdentification", messages);

                if (PBSRPBSItemCode != null && TherapeuticGoodIdentification.OriginalText.IsNullOrEmptyWhitespace())
                {
                    vb.AddValidationMessage(vb.PathName, null, "TherapeuticGoodIdentification's OriginalText is a required field when PBSRPBSItemCode is present");
                }

                if (TherapeuticGoodIdentification.Translations != null)
                {
                    vb.AddValidationMessage(vb.PathName, null, "Translations can not be set for TherapeuticGoodIdentification please use PBS/RPBS Item Code instead");
                }
            }

            if (StructuredDose != null)
            {
                StructuredDose.Validate(vb.Path + "StructuredDose", messages);
            }

            if (Timing != null)
            {
                Timing.Validate(vb.Path + "Timing", messages);

                if (Timing.TimingDescription.IsNullOrEmptyWhitespace())
                {
                    vb.AddValidationMessage(vb.PathName, string.Empty, "If TIMING is included, Timing Description SHALL be fully and automatically derived");
                }
            }

            if (PBSCloseTheGapBenefit != null)
            {
                PBSCloseTheGapBenefit.Validate(vb.Path + "PBSCloseTheGapBenefit", messages);
            }

            if (AdministrationDetails != null)
            {
                AdministrationDetails.Validate(vb.Path + "AdministrationDetails]", vb.Messages);
            }

            if (vb.ArgumentRequiredCheck("QuantityToDispense", QuantityToDispense))
            {
                QuantityToDispense.ValidateDispensingUnit(vb.Path + "QuantityToDispense", messages);
            }

            vb.ArgumentRequiredCheck("MaximumNumberOfRepeats", MaximumNumberOfRepeats);

            if (MinimumIntervalBetweenRepeats != null)
            {
                MinimumIntervalBetweenRepeats.Validate(vb.Path + "MinimumIntervalBetweenRepeats", messages);
            }

            vb.ArgumentRequiredCheck("PBSPrescriptionType", PBSPrescriptionType);

            if (vb.ArgumentRequiredCheck("MedicalBenefitCategoryType", MedicalBenefitCategoryType))
            {
                if (MedicalBenefitCategoryType.Value == Nehta.VendorLibrary.CDA.Common.Enums.MedicalBenefitCategoryType.CTG)
                {
                    vb.AddValidationMessage(vb.PathName, null, "Medical Benefit Category Type of CTG is not valid for this document");
                }
            }

            if (PBSRPBSItemCode != null)
            {
                PBSRPBSItemCode.Validate(vb.Path + "PBSRPBSItemCode", messages);
            }

            if (PBSRPBSManufacturerCode != null)
            {
                PBSRPBSManufacturerCode.Validate(vb.Path + "PBSRPBSManufacturerCode", messages);

                if (MedicalBenefitCategoryType.HasValue && !(MedicalBenefitCategoryType.Value == Nehta.VendorLibrary.CDA.Common.Enums.MedicalBenefitCategoryType.PBS ||
                                                             MedicalBenefitCategoryType.Value == Nehta.VendorLibrary.CDA.Common.Enums.MedicalBenefitCategoryType.RPBS))
                {
                    vb.AddValidationMessage(vb.PathName, null, "PBSRPBSManufacturerCode SHALL be present on an e-prescription where the Medical Benefit Type Category is one of the following: PBS  RPBS ");
                }
            }

            vb.ArgumentRequiredCheck("GroundsForConcurrentSupply", GroundsForConcurrentSupply);

            if (PBSExtemporaneousIngredient != null)
            {
                for (var x = 0; x < PBSExtemporaneousIngredient.Count; x++)
                {
                    PBSExtemporaneousIngredient[x].Validate(vb.Path + string.Format("PBSExtemporaneousIngredient[{0}]", x), vb.Messages);
                }
            }

            if (StateAuthorityNumber != null)
            {
                StateAuthorityNumber.Validate(vb.Path + "StateAuthorityNumber", messages);

                if (StateAuthorityNumber.Extension.IsNullOrEmptyWhitespace())
                {
                    vb.AddValidationMessage(vb.PathName, null, "Extension is required for StateAuthorityNumber");
                }
            }

            if (MedicationInstructionIdentifier != null)
            {
                MedicationInstructionIdentifier.Validate(vb.Path + "MedicationInstructionIdentifier", messages);
            }

            if (DispenseItemIdentifier != null)
            {
                DispenseItemIdentifier.Validate(vb.Path + "DispenseItemIdentifier", messages);
            }

            if (Observations != null)
            {
                Observations.Validate(vb.Path + "Observations", messages);
            }
        }