/// <summary>
        /// Set Derivation.
        /// </summary>
        public static ElementDefinition SetDerivation(this ElementDefinition elementDefinition,
                                                      StructureDefinition.TypeDerivationRule value)
        {
            String strValue = value.ToString().ToLower();

            elementDefinition.AddExtension(DerivationExtensionUri, new Code(strValue));
            return(elementDefinition);
        }