if n <= 0 {
		return "", "", s, ErrHeader
	}

	// Extract everything between the space and the final newline.
	rec, nl, rem := rest[:n-1], rest[n-1:n], rest[n:]
	if nl != "\n" {
		return "", "", s, ErrHeader
	}

	// The first equals separates the key from the value.
	k, v, ok = strings.Cut(rec, "=")
	if !ok {
		return "", "", s, ErrHeader
	}

	if !validPAXRecord(k, v) {
		return "", "", s, ErrHeader

			keys = append(keys, k)
		}
		sort.Strings(keys)

		// Write each record to a buffer.
		var buf strings.Builder
		for _, k := range keys {
			rec, err := formatPAXRecord(k, paxHdrs[k])
			if err != nil {
				return err
			}
			buf.WriteString(rec)
		}

		// Write the extended header file.
		var name string
		var flag byte
		if isGlobal {
			name = realName
			if name == "" {