afs:tag can be used to tag replies with the result of a boolean predicate. The parameter value must be of type "id":predicate where "id" is a user-specified identifier and predicate is a boolean predicate.
afs:tag has a behavior similar to afs:filter except that afs:filter discards replies where the predicate is evaluated to false, whereas afs:tag appends information to each reply. An afs:tag child element is added to each afs:reply. The afs:tag element has two attributes: