format.mayOnlyBe(FormatPAX)
	}
	if !isHeaderOnlyType(h.Typeflag) && h.Size < 0 {
		return FormatUnknown, nil, headerError{"negative size on header-only type"}
	}

	// Check PAX records.
	if len(h.Xattrs) > 0 {
		for k, v := range h.Xattrs {
			paxHdrs[paxSchilyXattr+k] = v
		}
		whyOnlyPAX = "only PAX supports Xattrs"
		format.mayOnlyBe(FormatPAX)
	}
	if len(h.PAXRecords) > 0 {