http://pubsubhubbub.appspot.com/

Developer(s): Google

Answers are:

Subscription

100: Supports subscriptions with hub.mode, hub.topic and hub.callback
101: Supports subscriptions with hub.mode, hub.topic, hub.callback and hub.secret
102: Ignores unrecognized parameters in the subscription request
103: Allows subscribers to re-request active subscriptions before they expire
104: Supports unsubscription requests
1xx: Sends a properly formatted verification request for subscribing and unsubscribing
Allows subscribers to request a specific lease duration
- If not, then describe the default lease duration issued, or other specifics here

(1xx denotes that you can can use any of the 100-104 tests to confirm this feature)