formats: FormatPAX | FormatGNU,
	}, {
		header:  &Header{ModTime: time.Unix(1, 500)},
		paxHdrs: map[string]string{paxMtime: "1.0000005"},
		formats: FormatUSTAR | FormatPAX | FormatGNU,
	}, {
		header:  &Header{ModTime: time.Unix(1, 0)},
		formats: FormatUSTAR | FormatPAX | FormatGNU,
	}, {
		header:  &Header{ModTime: time.Unix(1, 0), Format: FormatPAX},
		formats: FormatUSTAR | FormatPAX,
	}, {

				"uname":      strings.Repeat("long", 10),
			},
			Format: FormatPAX,
		}},
	}, {
		file: "testdata/pax-global-records.tar",
		headers: []*Header{{
			Typeflag:   TypeXGlobalHeader,
			Name:       "global1",
			PAXRecords: map[string]string{"path": "global1", "mtime": "1500000000.0"},
			Format:     FormatPAX,
		}, {
			Typeflag: TypeReg,
			Name:     "file1",
			ModTime:  time.Unix(0, 0),

		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 {

	// filenames larger than 256 characters, and non-ASCII filenames.
	//
	// Reference:
	//	http://pubs.opengroup.org/onlinepubs/9699919799/utilities/pax.html#tag_20_92_13_06
	FormatUSTAR

	// FormatPAX represents the PAX header format defined in POSIX.1-2001.
	//
	// PAX extends USTAR by writing a special file with Typeflag TypeXHeader
	// preceding the original header. This file contains a set of key-value

	// normally be visible to the outside. As such, this loop iterates through
	// one or more "header files" until it finds a "normal file".
	format := FormatUSTAR | FormatPAX | FormatGNU
	for {
		// Discard the remainder of the file and any padding.
		if err := discard(tr.r, tr.curr.physicalRemaining()); err != nil {
			return nil, err
		}

		}
		if err := tw.writeRawFile(name, data, flag, FormatPAX); err != nil || isGlobal {
			return err // Global headers return here
		}
	}

	// Pack the main header.
	var f formatter // Ignore errors since they are expected
	fmtStr := func(b []byte, s string) { f.formatString(b, toASCII(s)) }
	blk := tw.templateV7Plus(hdr, fmtStr, f.formatOctal)
	blk.setFormat(FormatPAX)