func ParseRegion(s string) (Region, error) {
	if n := len(s); n < 2 || 3 < n {
		return 0, ErrSyntax
	}
	var buf [3]byte
	return getRegionID(buf[:copy(buf[:], s)])
}
ParseRegion parses a 2- or 3-letter ISO 3166-1 or a UN M.49 code.
It returns a ValueError if s is a well-formed but unknown region identifier
or another error if another error occurred.
package language  
import (
	"errors"
	"fmt"
	"strings"
)
const (
	maxCoreSize = 12
	max99thPercentileSize = 32
	maxSimpleUExtensionSize = 14
)
type Tag struct {
	LangID   Language
	RegionID Region
	ScriptID Script
	pVariant byte    
	pExt     uint16  
	str string
}
func Make(s string) Tag {
	t, _ := Parse(s)
	return t
}
func (t Tag) Raw() (b Language, s Script, r Region) {
	return t.LangID, t.ScriptID, t.RegionID
}
func (t Tag) equalTags(a Tag) bool {
	return t.LangID == a.LangID && t.ScriptID == a.ScriptID && t.RegionID == a.RegionID
}
func (t Tag) IsRoot() bool {
	if int(t.pVariant) < len(t.str) {
		return false
	}
	return t.equalTags(Und)
}
func (t Tag) IsPrivateUse() bool {
	return t.str != "" && t.pVariant == 0
}
func (t *Tag) RemakeString() {
	if t.str == "" {
		return
	}
	extra := t.str[t.pVariant:]
	if t.pVariant > 0 {
		extra = extra[1:]
	}
	if t.equalTags(Und) && strings.HasPrefix(extra, "x-") {
		t.str = extra
		t.pVariant = 0
		t.pExt = 0
		return
	}
	var buf [max99thPercentileSize]byte  
	b := buf[:t.genCoreBytes(buf[:])]
	if extra != "" {
		diff := len(b) - int(t.pVariant)
		b = append(b, '-')
		b = append(b, extra...)
		t.pVariant = uint8(int(t.pVariant) + diff)
		t.pExt = uint16(int(t.pExt) + diff)
	} else {
		t.pVariant = uint8(len(b))
		t.pExt = uint16(len(b))
	}
	t.str = string(b)
}
func (t *Tag) genCoreBytes(buf []byte) int {
	n := t.LangID.StringToBuf(buf[:])
	if t.ScriptID != 0 {
		n += copy(buf[n:], "-")
		n += copy(buf[n:], t.ScriptID.String())
	}
	if t.RegionID != 0 {
		n += copy(buf[n:], "-")
		n += copy(buf[n:], t.RegionID.String())
	}
	return n
}
func (t Tag) String() string {
	if t.str != "" {
		return t.str
	}
	if t.ScriptID == 0 && t.RegionID == 0 {
		return t.LangID.String()
	}
	buf := [maxCoreSize]byte{}
	return string(buf[:t.genCoreBytes(buf[:])])
}
func (t Tag) MarshalText() (text []byte, err error) {
	if t.str != "" {
		text = append(text, t.str...)
	} else if t.ScriptID == 0 && t.RegionID == 0 {
		text = append(text, t.LangID.String()...)
	} else {
		buf := [maxCoreSize]byte{}
		text = buf[:t.genCoreBytes(buf[:])]
	}
	return text, nil
}
func (t *Tag) UnmarshalText(text []byte) error {
	tag, err := Parse(string(text))
	*t = tag
	return err
}
func (t Tag) Variants() string {
	if t.pVariant == 0 {
		return ""
	}
	return t.str[t.pVariant:t.pExt]
}
func (t Tag) VariantOrPrivateUseTags() string {
	if t.pExt > 0 {
		return t.str[t.pVariant:t.pExt]
	}
	return t.str[t.pVariant:]
}
func (t Tag) HasString() bool {
	return t.str != ""
}
func (t Tag) Parent() Tag {
	if t.str != "" {
		b, s, r := t.Raw()
		t = Tag{LangID: b, ScriptID: s, RegionID: r}
		if t.RegionID == 0 && t.ScriptID != 0 && t.LangID != 0 {
			base, _ := addTags(Tag{LangID: t.LangID})
			if base.ScriptID == t.ScriptID {
				return Tag{LangID: t.LangID}
			}
		}
		return t
	}
	if t.LangID != 0 {
		if t.RegionID != 0 {
			maxScript := t.ScriptID
			if maxScript == 0 {
				max, _ := addTags(t)
				maxScript = max.ScriptID
			}
			for i := range parents {
				if Language(parents[i].lang) == t.LangID && Script(parents[i].maxScript) == maxScript {
					for _, r := range parents[i].fromRegion {
						if Region(r) == t.RegionID {
							return Tag{
								LangID:   t.LangID,
								ScriptID: Script(parents[i].script),
								RegionID: Region(parents[i].toRegion),
							}
						}
					}
				}
			}
			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 {
			base, _ := addTags(Tag{LangID: t.LangID})
			if base.ScriptID != t.ScriptID {
				return Und
			}
			return Tag{LangID: t.LangID}
		}
	}
	return Und
}
func ParseExtension(s string) (ext string, err error) {
	scan := makeScannerString(s)
	var end int
	if n := len(scan.token); n != 1 {
		return "", ErrSyntax
	}
	scan.toLower(0, len(scan.b))
	end = parseExtension(&scan)
	if end != len(s) {
		return "", ErrSyntax
	}
	return string(scan.b), nil
}
func (t Tag) HasVariants() bool {
	return uint16(t.pVariant) < t.pExt
}
func (t Tag) HasExtensions() bool {
	return int(t.pExt) < len(t.str)
}
func (t Tag) Extension(x byte) (ext string, ok bool) {
	for i := int(t.pExt); i < len(t.str)-1; {
		var ext string
		i, ext = getExtension(t.str, i)
		if ext[0] == x {
			return ext, true
		}
	}
	return "", false
}
func (t Tag) Extensions() []string {
	e := []string{}
	for i := int(t.pExt); i < len(t.str)-1; {
		var ext string
		i, ext = getExtension(t.str, i)
		e = append(e, ext)
	}
	return e
}
func (t Tag) TypeForKey(key string) string {
	if start, end, _ := t.findTypeForKey(key); end != start {
		return t.str[start:end]
	}
	return ""
}
var (
	errPrivateUse       = errors.New("cannot set a key on a private use tag")
	errInvalidArguments = errors.New("invalid key or type")
)
func (t Tag) SetTypeForKey(key, value string) (Tag, error) {
	if t.IsPrivateUse() {
		return t, errPrivateUse
	}
	if len(key) != 2 {
		return t, errInvalidArguments
	}
	if value == "" {
		start, end, _ := t.findTypeForKey(key)
		if start != end {
			start -= 4
			if (end == len(t.str) || t.str[end+2] == '-') && t.str[start-2] == '-' {
				start -= 2
			}
			if start == int(t.pVariant) && end == len(t.str) {
				t.str = ""
				t.pVariant, t.pExt = 0, 0
			} else {
				t.str = fmt.Sprintf("%s%s", t.str[:start], t.str[end:])
			}
		}
		return t, nil
	}
	if len(value) < 3 || len(value) > 8 {
		return t, errInvalidArguments
	}
	var (
		buf    [maxCoreSize + maxSimpleUExtensionSize]byte
		uStart int  
	)
	if t.str == "" {
		uStart = t.genCoreBytes(buf[:])
		buf[uStart] = '-'
		uStart++
	}
	b := buf[uStart:]
	copy(b, "u-")
	copy(b[2:], key)
	b[4] = '-'
	b = b[:5+copy(b[5:], value)]
	scan := makeScanner(b)
	if parseExtensions(&scan); scan.err != nil {
		return t, scan.err
	}
	if t.str == "" {
		t.pVariant, t.pExt = byte(uStart-1), uint16(uStart-1)
		t.str = string(buf[:uStart+len(b)])
	} else {
		s := t.str
		start, end, hasExt := t.findTypeForKey(key)
		if start == end {
			if hasExt {
				b = b[2:]
			}
			t.str = fmt.Sprintf("%s-%s%s", s[:start], b, s[end:])
		} else {
			t.str = fmt.Sprintf("%s%s%s", s[:start], value, s[end:])
		}
	}
	return t, nil
}
func (t Tag) findTypeForKey(key string) (start, end int, hasExt bool) {
	p := int(t.pExt)
	if len(key) != 2 || p == len(t.str) || p == 0 {
		return p, p, false
	}
	s := t.str
	for p++; s[p] != 'u'; p++ {
		if s[p] > 'u' {
			p--
			return p, p, false
		}
		if p = nextExtension(s, p); p == len(s) {
			return len(s), len(s), false
		}
	}
	p++
	curKey := ""
	for {
		if p3 := p + 3; s[p3] == '-' {
			if curKey == key {
				return start, p, true
			}
			curKey = s[p+1 : p3]
			if curKey > key {
				return p, p, true
			}
			start = p + 4
			p += 7  
		} else {
			p += 4
		}
		max := p + 5  
		if len(s) < max {
			max = len(s)
		}
		for ; p < max && s[p] != '-'; p++ {
		}
		if p == len(s) || s[p+2] == '-' {
			if curKey == key {
				return start, p, true
			}
			return p, p, true
		}
	}
}
func ParseBase(s string) (Language, error) {
	if n := len(s); n < 2 || 3 < n {
		return 0, ErrSyntax
	}
	var buf [3]byte
	return getLangID(buf[:copy(buf[:], s)])
}
func ParseScript(s string) (Script, error) {
	if len(s) != 4 {
		return 0, ErrSyntax
	}
	var buf [4]byte
	return getScriptID(script, buf[:copy(buf[:], s)])
}
func EncodeM49(r int) (Region, error) {
	return getRegionM49(r)
}