Return true if the x is a recognised actor type, else false.

Return nil if validating one of these options returns nil; otherwise return a list comprising a fault report object with this severity-if-none and this token followed by all the fault reports from validating each option.

There are several places - but especially in validating collections - where there are several different valid configurations, but few or no properties are always required.

As object-reference-or-fault, except value argument may also be a list of objects and/or object references.

Quick function to replace the pattern (nil-if-empty (remove nil? (concat …))) which I’m using a lot!

If v is false or nil, return a fault object with this severity and token, else return nil.

Returns true iff x quacks like an ActivityStreams context, else false.

A context is either 1. the URI (actually an IRI) activitystreams-context-uri, or 2. a collection comprising that URI and a map.

Return a list of reports taken from these reports where the severity of the report is greater than this or equal to this severity.

Return true if the object x has a type which is an activity type, else false.

Return true if the object x has a type which is an actor type, else false.

True if x is an ActivityStreams object with a valid context, else false.

If object x has a :type value which is acceptable, return nil; else return a fault object with this severity and token.

acceptable may be passed as either nil, a string, or a set of strings. If acceptable is nil, no type specific tests will be performed.

Return true if object x has type type, else false.

The values of type fields of ActivityStreams objects may be lists; they are considered to have a type if the type token is a member of the list.

Very basic check that x is either a link object or a URI.

Return a fault object with these severity, fault and narrative values.

An ActivityPub object MUST have a globally unique ID. Whether this is meaningful depends on whether we persist fault report objects and serve them, which at present I have no plans to do.

if x is an empty collection, return nil; else return x.

Return a list of faults found in object x, or nil if none are.

If expected-type is also passed, verify that x has expected-type. expected-type may be passed as a string or as a set of strings. Detailed verification of the particular features of types is not done here.

Very basic check that x is either an object or a URI.

If this value is either

1. an object of expected-type;
2. a URI referencing an object of expected-type; or
3. a link object referencing an object of expected-type

and no faults are returned from validating the linked object, then return nil; else return a sequence comprising a fault object with this severity and token, prepended to the faults returned.

As with has-type-or-fault (q.v.), expected-type may be passed as a string, as a set of strings, or nil (indicating the type of the referenced object should not be checked).

NOTE THAT if *reify-refs* is false, referenced objects will not actually be checked.

If this value is not a string, return a fault object with this severity and token, else nil. If pattern is also passed, it is expected to be a Regex, and the fault object will be returned unless value matches the pattern.

Return true if x is truthy, else false. There must be some more idiomatic way to do this?

true if x, a string, represents a recognised ActivityStreams activity type.