Takes the name of a spec/predicate-returning multimethod and a tag-restoring keyword or fn (retag). Returns a spec that when conforming or explaining data will pass it to the multimethod to get an appropriate spec. You can e.g. use multi-spec to dynamically and extensibly associate specs with 'tagged' data (i.e. data where one of the fields indicates the shape of the rest of the structure). (defmulti mspec :tag) The methods should ignore their argument and return a predicate/spec: (defmethod mspec :int [_] (s/keys :req-un [::tag ::i])) retag is used during generation to retag generated values with matching tags. retag can either be a keyword, at which key the dispatch-tag will be assoc'ed, or a fn of generated value and dispatch-tag that should return an appropriately retagged value. Note that because the tags themselves comprise an open set, the tag key spec cannot enumerate the values, but can e.g. test for keyword?. Note also that the dispatch values of the multimethod will be included in the path, i.e. in reporting and gen overrides, even though those values are not evident in the spec.