Indicates whether the current instance of the System.Web.UI.Design.SupportsPreviewControlAttribute class is set to the default preview attribute value.
true if the current instance of System.Web.UI.Design.SupportsPreviewControlAttribute is equal to the default preview attribute value; otherwise, false.
The SupportsPreviewControlAttribute.IsDefaultAttribute method compares the value for the SupportsPreviewControlAttribute.SupportsPreviewControl property of the current System.Web.UI.Design.SupportsPreviewControlAttribute object with the value for the SupportsPreviewControlAttribute.SupportsPreviewControl property of the static SupportsPreviewControlAttribute.Default field.