scan.toLower(0, len(scan.b))
		if n == 0 || scan.token[0] != 'x' {
			return t, ErrSyntax
		}
		end = parseExtensions(scan)
	} else if n >= 4 {
		return Und, ErrSyntax
	} else { // the usual case
		t, end = parseTag(scan, true)
		if n := len(scan.token); n == 1 {
			t.pExt = uint16(end)
			end = parseExtensions(scan)
		} else if end < len(scan.b) {
			scan.setError(ErrSyntax)
			scan.b = scan.b[:end]
		}
	}

			if base.ScriptID != t.ScriptID {
				return Und
			}
			return Tag{LangID: t.LangID}
		}
	}
	return Und
}

// ParseExtension parses s as an extension and returns it on success.
func ParseExtension(s string) (ext string, err error) {
	defer func() {
		if recover() != nil {
			ext = ""
			err = ErrSyntax
		}
	}()

	scan := makeScannerString(s)

// type tag.
func (e Extension) String() string {
	return e.s
}

// ParseExtension parses s as an extension and returns it on success.
func ParseExtension(s string) (e Extension, err error) {
	ext, err := language.ParseExtension(s)
	return Extension{ext}, err
}

// Type returns the one-byte extension type of e. It returns 0 for the zero
// exception.

		return time.Time{}, time.Time{}, err
	}
	notAfter, err := parseTime(&der)
	if err != nil {
		return time.Time{}, time.Time{}, err
	}

	return notBefore, notAfter, nil
}

func parseExtension(der cryptobyte.String) (pkix.Extension, error) {
	var ext pkix.Extension
	if !der.ReadASN1ObjectIdentifier(&ext.Id) {
		return ext, errors.New("x509: malformed extension OID field")
	}