/// <summary>
        /// Determines if the given value represents a valid state of this property.
        /// </summary>
        /// <param name="value">The state that should be used.</param>
        /// <returns>True if the state is valid, otherwise false.</returns>
        protected override Boolean IsValid(CSSValue value)
        {
            if (value.Is(Keywords.None))
            {
                _properties.Clear();
            }
            else if (value is CSSPrimitiveValue)
            {
                var property = value.ToAnimatableIdentifier();

                if (property == null)
                {
                    return(false);
                }

                _properties.Clear();
                _properties.Add(property);
            }
            else if (value is CSSValueList)
            {
                var properties = value.AsList(ValueExtensions.ToAnimatableIdentifier);

                if (properties == null)
                {
                    return(false);
                }

                _properties.Clear();
                _properties.AddRange(properties);
            }
            else
            {
                return(false);
            }

            return(true);
        }