}
	(*s)[uniqueName{key, name, level}] = pos
}

var checkTagDups = []string{"json", "xml"}
var checkTagSpaces = map[string]bool{"json": true, "xml": true, "asn1": true}

// checkCanonicalFieldTag checks a single struct field tag.
func checkCanonicalFieldTag(pass *analysis.Pass, field *types.Var, tag string, seen *namesSeen) {
	switch pass.Pkg.Path() {
	case "encoding/json", "encoding/xml":
		// These packages know how to use their own APIs.