in wfn/matching.go [315:332]
func CompareAttr(src, tgt string) (Relation, error) {
if src != NA && src != Any && HasWildcard(tgt) {
return Disjoint, fmt.Errorf("target attribute value cannot contain wildcard")
}
if src == tgt {
return Equal, nil
}
if src == Any {
return Superset, nil
}
if tgt == Any {
return Subset, nil
}
if src == NA || tgt == NA {
return Disjoint, nil
}
return matchStr(src, tgt), nil
}