Unblocking is not explained in the specification

The specification does not currently include a section on the "unblock" action which is mentioned in two other places in the specification, including the "Actions" list at https://indieweb.org/Microsub-spec#Actions.

While one could assume what an unblocking request should look like given the structure of the mute and unmute functions which are relatively similar, the spec should clarify exactly how one should go about issuing an Unblock request.

Read the Microsub specification's Actions list and the existing mute and unmute sections, then determine how the referenced unblock action should be issued. Document the Unblock request clearly in the specification, including the details needed to make its behavior unambiguous.

Written by the indexing model from the issue text.