A String value specifying the URL for the file that contains a detailed description for the chart.
The DescriptionUrl property specifies an HTML file that provides additional details for the WebChartControl. The DescriptionUrl property renders as the longdesc attribute for the web chart. If this property is not set, or is set to an empty string (""), the WebChartControl is rendered without the longdesc attribute. Use the DescriptionUrl property to supplement the WebChartControl.AlternateText property.