if t.equalTags(Und) {
		return t, nil
	}
	max, err := addTags(t)
	if err != nil {
		return t, err
	}
	for _, id := range [...]Tag{
		{LangID: t.LangID},
		{LangID: t.LangID, RegionID: t.RegionID},
		{LangID: t.LangID, ScriptID: t.ScriptID},
	} {
		if x, err := addTags(id); err == nil && max.equalTags(x) {
			t.setTagsFrom(id)
			break
		}
	}
	return t, nil

			base, _ := addTags(Tag{LangID: t.LangID})
			if base.ScriptID != maxScript {
				return Tag{LangID: t.LangID, ScriptID: maxScript}
			}
			return Tag{LangID: t.LangID}
		} else if t.ScriptID != 0 {
			// The parent for an base-script pair with a non-default script is
			// "und" instead of the base language.
			base, _ := addTags(Tag{LangID: t.LangID})
			if base.ScriptID != t.ScriptID {
				return Und

	}
	changed := false
	if c&SuppressScript != 0 {
		if t.LangID.SuppressScript() == t.ScriptID {
			t.ScriptID = 0
			changed = true
		}
	}
	if c&canonLang != 0 {
		for {
			if l, aliasType := t.LangID.Canonicalize(); l != t.LangID {
				switch aliasType {
				case language.Legacy:
					if c&Legacy != 0 {
						if t.LangID == _sh && t.ScriptID == 0 {
							t.ScriptID = _Latn
						}

func GetCompactCore(t Tag) (cci CompactCoreInfo, ok bool) {
	if t.LangID > langNoIndexOffset {
		return 0, false
	}
	cci |= CompactCoreInfo(t.LangID) << (8 + 12)
	cci |= CompactCoreInfo(t.ScriptID) << 12
	cci |= CompactCoreInfo(t.RegionID)
	return cci, true
}

// Tag generates a tag from c.
func (c CompactCoreInfo) Tag() Tag {
	return Tag{
		LangID:   Language(c >> 20),
		RegionID: Region(c & 0x3ff),

	// Don't change the language once we already have found an exact match.
	if m.pinLanguage && tag.LangID != m.want.LangID {
		return
	}
	// Pin the region group if we are comparing tags for the same language.
	if tag.LangID == m.want.LangID && m.sameRegionGroup {
		_, sameGroup := regionGroupDist(m.pinnedRegion, have.maxRegion, have.maxScript, m.want.LangID)
		if !sameGroup {
			return
		}
	}

		v /= base
	}
}

// getLangISO3 returns the langID for the given 3-letter ISO language code
// or unknownLang if this does not exist.
func getLangISO3(s []byte) (Language, error) {
	if tag.FixCase("und", s) {
		// first try to match canonical 3-letter entries
		for i := lang.Index(s[:2]); i != -1; i = lang.Next(s[:2], i) {
			if e := lang.Elem(i); e[3] == 0 && e[2] == s[2] {

	// TODO: use parent lookup table once cycle from internal package is
	// removed. Probably by internalizing the table and declaring this fast
	// enough.
	// lang := compactID(internal.Parent(uint16(t.language)))
	lang, _ := FromTag(t.language.Tag().Parent())
	return Tag{language: lang, locale: lang}
}

// nextToken returns token t and the rest of the string.
func nextToken(s string) (t, tail string) {
	p := strings.Index(s[1:], "-")

		t.str = b.private
		t.RemakeString()
	}
	return t
}

// SetTag copies all the settings from a given Tag. Any previously set values
// are discarded.
func (b *Builder) SetTag(t Tag) {
	b.Tag.LangID = t.LangID
	b.Tag.RegionID = t.RegionID
	b.Tag.ScriptID = t.ScriptID
	// TODO: optimize
	b.variants = b.variants[:0]
	if variants := t.Variants(); variants != "" {
		for _, vr := range strings.Split(variants[1:], "-") {

func update(b *language.Builder, part ...interface{}) (err error) {
	for _, x := range part {
		switch v := x.(type) {
		case Tag:
			b.SetTag(v.tag())
		case Base:
			b.Tag.LangID = v.langID
		case Script:
			b.Tag.ScriptID = v.scriptID
		case Region:
			b.Tag.RegionID = v.regionID
		case Variant:
			if v.variant == "" {
				err = errInvalidArgument
				break
			}

type bases []Base

func (b bases) Len() int {
	return len(b)
}

func (b bases) Swap(i, j int) {
	b[i], b[j] = b[j], b[i]
}

func (b bases) Less(i, j int) bool {
	return b[i].langID < b[j].langID
}

// BaseLanguages returns the result from calling s.bases if it is specified or
// otherwise derives the set of supported base languages from tags.
func (s *coverage) BaseLanguages() []Base {