Represents the collection of extensibility elements used by the XML Web service. This class cannot be inherited.
This collection can either contain instances of classes deriving from System.Web.Services.Description.ServiceDescriptionFormatExtension, or instances of the System.Xml.XmlElement class. In a derived class, System.Web.Services.Description.ServiceDescriptionFormatExtension class allows users to define extensibility elements in addition to those defined in the Web Services Description Language (WSDL) specification. Use these in your System.Web.Services.Description.ServiceDescriptionFormatExtensionCollection if you know in advance the type of extensibility element you want to make. Use an System.Xml.XmlElement when you do not know the format of an element in advance.