Why HttpRequest.HttpMethod is string instead of Enum?

Question

In the Reference of HttpRequest.HttpMethod of .NET Framework, request type is declared with System.String type.

In RFC 2616 all HTTP request methods are

Answer 1

if HTTP Comes with a new method, then java and C# needs to update their enum. When will they update it? Will they release a patch? or will be updated in next version? So defining a enum on values which they dont control is not a wise decision.