Actions have the following slots:

rest	A parameter name to map the rest of the URL, after the action name, to. If this is not set, then navigating to a URL where the action is not the last path component will return to the client with an error. A more general facility can be found in the http.server.rewrite vocabulary.
init	A quotation called at the beginning of a GET, HEAD or DELETE request. Typically this quotation configures HTML forms and parses query parameters.
authorize	A quotation called at the beginning of all implemented requests. In GET, HEAD and DELETE requests, it is called after the init quotation; in PATCH, POST and PUT requests, it is called after the validate quotation. By convention, this quotation performs custom authorization checks which depend on query parameters or POST parameters.
display	A quotation called after the init quotation in a GET request. This quotation must return an HTTP response.
validate	A quotation called at the beginning of a POST request to validate POST parameters.
submit	A quotation called after the validate quotation in a POST request. This quotation must return an HTTP response.
replace	A quotation called after the validate quotation in a PUT request. This quotation must return an HTTP response.
update	A quotation called after the validate quotation in a PATCH request. This quotation must return an HTTP response.
delete	A quotation called after the init quotation in a DELETE request. This quotation must return an HTTP response.

At least one of the display and submit slots must be set, otherwise the action will be useless.