if !ok {
		return "", "", s, ErrHeader
	}

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

// formatPAXRecord formats a single PAX record, prefixing it with the
// appropriate length.
func formatPAXRecord(k, v string) (string, error) {
	if !validPAXRecord(k, v) {
		return "", ErrHeader
	}

				paxHdrs[k] = v // Ignore local records that may conflict
			}
		}
		whyOnlyPAX = "only PAX supports PAXRecords"
		format.mayOnlyBe(FormatPAX)
	}
	for k, v := range paxHdrs {
		if !validPAXRecord(k, v) {
			return FormatUnknown, nil, headerError{fmt.Sprintf("invalid PAX record: %q", k+" = "+v)}
		}
	}

	// TODO(dsnet): Re-enable this when adding sparse support.
	// See https://golang.org/issue/22735