return tt, nil
					}
					// Even if we fail to find a unique Region, we might have
					// an unambiguous script.
					if goodScript {
						t.ScriptID = tt.ScriptID
					}
				}
			}
		}
	} else {
		// Search matches for und-script.
		if t.ScriptID != 0 {
			x := likelyScript[t.ScriptID]
			if x.region != 0 {
				t.setUndefinedRegion(Region(x.region))
				t.setUndefinedLang(Language(x.lang))

			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

// GetCompactCore generates a uint32 value that is guaranteed to be unique for
// different language, region, and script values.
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.

	sc, err := language.ParseScript(s)
	return Script{sc}, err
}

// String returns the script code in title case.
// It returns "Zzzz" for an unspecified script.
func (s Script) String() string {
	return s.scriptID.String()
}

// IsPrivateUse reports whether this script code is reserved for private use.
func (s Script) IsPrivateUse() bool {
	return s.scriptID.IsPrivateUse()
}

		tt = m.default_.tag
		if m.preferSameScript {
		outer:
			for _, w := range want {
				script, _ := w.Script()
				if script.scriptID == 0 {
					// Don't do anything if there is no script, such as with
					// private subtags.
					continue
				}
				for i, h := range m.supported {
					if script.scriptID == h.maxScript {
						tt, index = h.tag, i
						break outer
					}
				}
			}
		}

	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:], "-") {
			b.variants = append(b.variants, vr)
		}
	}

		// Deal with cases where an extra script is inserted for the region.
		t, _ := t.Maximize()
		if x, ok := getCoreIndex(t); ok {
			return x, exact
		}
	}
	for t = t.Parent(); t != root; t = t.Parent() {
		// No variants specified: just compare core components.
		// The key has the form lllssrrr, where l, s, and r are nibbles for
		// respectively the langID, scriptID, and regionID.
		if x, ok := getCoreIndex(t); ok {

	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
			}
			b.AddVariant(v.variant)
		case Extension:

				scan.start = langStart + len(langStr) + 1
			}
			scan.gobble(e)
		}
		end = scan.scan()
	}
	if len(scan.token) == 4 && isAlpha(scan.token[0]) {
		t.ScriptID, e = getScriptID(script, scan.token)
		if t.ScriptID == 0 {
			scan.gobble(e)
		}
		end = scan.scan()
	}
	if n := len(scan.token); n >= 2 && n <= 3 {
		t.RegionID, e = getRegionID(scan.token)
		if t.RegionID == 0 {

func newScriptEngine() *script.Engine {
	conds := script.DefaultConds()

	interrupt := func(cmd *exec.Cmd) error { return cmd.Process.Signal(os.Interrupt) }
	gracePeriod := 30 * time.Second // arbitrary

	cmds := script.DefaultCmds()
	cmds["at"] = scriptAt()
	cmds["bzr"] = script.Program("bzr", interrupt, gracePeriod)
	cmds["fossil"] = script.Program("fossil", interrupt, gracePeriod)