}
		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
	/*
		// Check sparse files.