No one really knows what a cloud is. It is vaguely documented in SOAP meets RSS.
The domain of the cloud. Should be just the domain name, not including the http:// protocol. All clouds are presumed to operate over HTTP. The cloud specification does not support secure clouds over HTTPS, nor can clouds operate over other protocols.
The port of the cloud. Should be an integer, but Universal Feed Parser currently returns it as a string.
The protocol of the cloud. Documentation differs on what the acceptable values are. Acceptable values definitely include xml-rpc and soap, although only in lowercase, despite both being acronyms.
There is no way for a publisher to specify the version number of the protocol to use. soap refers to SOAP 1.1; the cloud interface does not support SOAP 1.0 or 1.2.
post or http-post might also be acceptable values; nobody really knows for sure.