NT/base/fs/utils/regedit/regporte.c:471

    Sit back, and I will tell ye a tale of woe.

    Win95 and NT 4 shipped with regedit compiled ANSI.  There are a couple
    of registry types on NT (namely REG_EXPAND_SZ and REG_MULTI_SZ) that
    weren't on Win95, and which regedit doesn't really understand.  regedit
    treats these registry types as hex binary streams.

    You can probably see where this is going.

    If you exported, say your user TEMP environment variable on NT 4
    using regedit, you'd get something that looked like this:

REGEDIT4

[HKEY_CURRENT_USER\Environment]
"TEMP"=hex(2):25,53,59,53,54,45,4d,44,52,49,56,45,25,5c,53,48,54,65,6d,70,00

    ...a nice, null-terminated ANSI string.  Nice, that is, until we decided
    to compile regedit UNICODE for NT 5.  A unicode regedit exports your
    user TEMP variable like this:

REGEDIT4

[HKEY_CURRENT_USER\Environment]
"TEMP"=hex(2):25,00,53,00,59,00,53,00,54,00,45,00,4d,00,44,00,52,00,49,00,56,\
  00,45,00,25,00,5c,00,53,00,48,00,54,00,65,00,6d,00,70,00,00,00

    ...mmmm.  Unicode.  Of course, a unicode regedit also expects anything
    it imports to have all those interspersed zeroes, too.  Otherwise,
    it dumps garbage into your registry.  All it takes is a -DUNICODE, and
    regedit is suddenly incompatible with the thousdands of existing .reg
    files out there.

    So just bump the version in the header to REGEDIT5 and be done with
    it, right?  Wrong.  The regedit on Win95 and NT 4 looks at the first
    character after the string "REGEDIT" and compares it to the digit "4".
    If that character is anything other than the digit "4", the parser
    assumes it is looking at a Windows 3.1 file.  Yep.  There will only
    ever be two formats, right?  Just Win95 and Win3.1.  That's all the
    world needs.

    So a completely new .reg file header had to be invented, so that the
    older, regedits of the world would simply regect the new,
    unicodized .reg files outright.  An NT 5 .reg file, exporting your user
    TEMP variable, looks like this:

Windows Registry Editor Version 5.00

[HKEY_CURRENT_USER\Environment]
"TEMP"=hex(2):25,00,53,00,59,00,53,00,54,00,45,00,4d,00,44,00,52,00,49,00,56,\
  00,45,00,25,00,5c,00,53,00,48,00,54,00,65,00,6d,00,70,00,00,00

    The parser is still not very good, but it does bother to convert that 5.00
    into a version number, so that future generations can bump it to 5.50 or
    6.00, and the regedit 5.00 that shipped with NT 5.00 will properly reject
    the files.