If the browser does not recognize cache control directives or extensions, the browser must ignore the unrecognized terms. For more information, see RFC 2616: Hypertext Transfer Protocol -- HTTP/1.1, available on the tp://go.microsoft.com/fwlink/?linkid=37125.
HttpCachePolicy.AppendCacheExtension(string) is introduced in the .NET Framework version 3.5. For more information, see The .NET Framework 3.5 Architecture.