Defining new methods for REST services - is this valid HTTP?

According to the HTTP protocol, the list of methods can be expanded:

9 Method Definitions

The set of common methods for HTTP/1.1 is defined below. Although this set can be expanded, additional methods cannot be assumed to share the same semantics for separately extended clients and servers.

Does that mean that if I write the client and server and define a new method, 开发者_运维百科this is a valid HTTP 1.1 request?

FROB /some/url HTTP/1.1
Host: www.example.com

Clearly "old" http clients wouldn't support this new method and it would only be an extension for the "new" client I'm writing, but my question is about the semantics of the standard and not actual implementation.