/// <summary>
        /// Gets the single <see cref="SubstituteType"/> from the <see cref="IArgumentNullExceptionFixture.Mappings"/>.
        /// </summary>
        /// <param name="fixture">The fixture.</param>
        /// <returns>The single <see cref="SubstituteType"/> from the
        /// <see cref="IArgumentNullExceptionFixture.Mappings"/>.</returns>
        /// <exception cref="ArgumentNullException">The <paramref name="fixture"/> parameter is
        /// <see langword="null"/>.</exception>
        /// <exception cref="InvalidOperationException">There are zero of more than one <see cref="SubstituteType"/>
        /// objects in the <see cref="IArgumentNullExceptionFixture.Filters"/>.</exception>
        private static SubstituteType GetSubstituteTypeMapping(this IArgumentNullExceptionFixture fixture)
        {
            if (fixture == null)
            {
                throw new ArgumentNullException(nameof(fixture));
            }

            SubstituteType substituteType =
                fixture.Mappings
                .OfType <SubstituteType>()
                .SingleOrDefault();

            if (substituteType == null)
            {
                throw new InvalidOperationException("There is no SubstituteType in the mappings.");
            }

            return(substituteType);
        }
 /// <summary>
 /// 自定義HTML內容注入屬性構造函數
 /// </summary>
 /// <param name="source">注入點</param>
 /// <param name="target">取得注入點</param>
 public SubstituteAttribute(SubstituteType source, string target)
 {
     _source = source;
     _target = target;
 }