n = 8
	}
	return e.v[:n]
}

// Error implements the error interface.
func (e ValueError) Error() string {
	return fmt.Sprintf("language: subtag %q is well-formed but unknown", e.tag())
}

// Subtag returns the subtag for which the error occurred.
func (e ValueError) Subtag() string {
	return string(e.tag())
}

// scanner is used to scan BCP 47 tokens, which are separated by _ or -.
type scanner struct {
	b     []byte

// result is deemed as good as its weakest link).
// We define the following levels:
//   Exact    - An exact match of a subtag, before adding likely subtags.
//   MaxExact - An exact match of a subtag, after adding likely subtags.
//              [See Note 2].
//   High     - High level of mutual intelligibility between different subtag
//              variants.

	return sort.Search(len(imap), func(i int) bool {
		return imap[i] >= key
	})
}

type Language uint16

// getLangID returns the langID of s if s is a canonical subtag
// or langUnknown if s is not a canonical subtag.
func getLangID(s []byte) (Language, error) {
	if len(s) == 2 {
		return getLangISO2(s)
	}
	return getLangISO3(s)
}

	// Normalize legacy encodings. This includes legacy languages defined in
	// CLDR as well as bibliographic codes defined in ISO-639.
	Legacy
	// Map the dominant language of a macro language group to the macro language
	// subtag. For example cmn -> zh.
	Macro
	// The CLDR flag should be used if full compatibility with CLDR is required.
	// There are a few cases where language.Tag may differ from CLDR. To follow all

// tag and length bytes) into out, sets outTag to its tag, and advances.
// It reports whether the read was successful.
//
// Tags greater than 30 are not supported (i.e. low-tag-number format only).
func (s *String) ReadAnyASN1(out *String, outTag *asn1.Tag) bool {
	return s.readASN1(out, outTag, true /* skip header */)
}

// attempt to infer their values.
// TODO: consider removing
func (t Tag) Raw() (b Language, s Script, r Region) {
	return t.LangID, t.ScriptID, t.RegionID
}

// equalTags compares language, script and region subtags only.
func (t Tag) equalTags(a Tag) bool {
	return t.LangID == a.LangID && t.ScriptID == a.ScriptID && t.RegionID == a.RegionID
}

// IsRoot returns true if t is equal to language "und".
func (t Tag) IsRoot() bool {