/// <summary>
        /// RevealModeProperty property changed handler.
        /// </summary>
        /// <param name="d">ExpandableContentControl that changed its RevealMode.</param>
        /// <param name="e">Event arguments.</param>
        private static void OnRevealModePropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            ExpandableContentControl source = (ExpandableContentControl)d;
            ExpandDirection          value  = (ExpandDirection)e.NewValue;

            if (value != ExpandDirection.Down &&
                value != ExpandDirection.Left &&
                value != ExpandDirection.Right &&
                value != ExpandDirection.Up)
            {
                // revert to old value
                source.RevealMode = (ExpandDirection)e.OldValue;

                string message = string.Format(
                    CultureInfo.InvariantCulture,
                    Properties.Resources.Expander_OnExpandDirectionPropertyChanged_InvalidValue,
                    value);
                throw new ArgumentException(message, "e");
            }

            // set the non-reveal dimension
            source.SetNonRevealDimension();

            // calculate the reveal dimension
            source.SetRevealDimension();
        }
        /// <summary>
        /// PercentageProperty property changed handler.
        /// </summary>
        /// <param name="d">Page that changed its Percentage.</param>
        /// <param name="e">Event arguments.</param>
        private static void OnPercentagePropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            ExpandableContentControl source = (ExpandableContentControl)d;

            source.SetRevealDimension();
        }