* References:
    * svx/source/msfilter/msvbasic.cxx
    * Costin Raiu, Kaspersky Labs, 'Apple of Discord'
    * Virus bulletin's bontchev.pdf, svajcer.pdf

Using a hacked libgsf's test-cp-msole.c:

      * round-trip - works fine, 'security warning from OXP'
      * deleting the __SRP_* streams: works fine ...

'Simple' stream:
      * Simple: 'SGetThree' -> 'SGetThack' - no pcode changes ...
	    + no visible changes
      * Compressed text:
	    + 0d 0a is the VBA test line terminator
	    + Screwing up the compression can cause _serious_
	      artefacts - ie. Excel loop/lock / crash etc.
      * VBA 5 -> VBA 6 ... (?)
      * pcode line table start marker: FE CA 01 00
	    + following 2 bytes : seemingly not a clobberable version.
	    + blanking (0x00) pcode between 42 81 0C 00 and ff ff ff ff -
	      gives empty 1st macro in spreadsheet.
	    + clobbering with 0xff's results in XP crasher.
      * clobbering the pcode results in the text changing ie.
	   For i = 0 To 10 -> For i = 0 To 31 - with no other change.
      * clobbered pcode with 0's from & inc. feca0100
      * ie. pcode totally ignored.
      * Can totally wipe all data from start to "01 ae b0 00'A''t''t',"
	none of it used (seemingly)
      * Can totally wipe all data _except_ pre-pended 3 items:
        0x01 0xae 0xb0 - as long as we update offsets in 'dir' stream;
	see later.
      * re-compressing seems to cause some nasty grief;
        _looks_ like a length is stored somewhere here.
	Our version is shrunk by N bytes, - we get N bytes of
	de-compressed crud at the end of the macro.

'_VBA_PROJECT' stream:
      * clobber byte 3 of _VBA_PROJECT to 0xa8 - also works going backwards: 0x01
	    + no need to clobber pcode table ... [ presumably not read !? ]
      * Office XP only requires this data in this file:
	    + cc 61 <01> 00 00 01 + pad to 32 bytes with 0s.
      * clobber macro name - reflected in re-load in
	    <module-name> [functions] list - ordering odd there though.

Generic stream description:
    + first byte '1'
    + 2nd byte == length of compressed data - 1
    + 3rd byte == 0xb + 4 bits MSB of compressed data length
	+ maximum recorded compressed size is 0xc0c ie 0x010cbc
	  above which it (appears) that it reads to the EOS.
    + 4th ... bytes = LZSS compressed macro text.
    + VBA editor can't cope with unicode - just barfs
	+ VBA editor can cope with 8bit chars - and writes them
	  out as such too.
    + can insert invalid / broken VBA with no problems.

All streams contain compressed text:
    + Sheet / Workbook / VBA etc. all re-constructed ... [!]

'dir' stream:
    * Looks like the project stream - but more authoritative ?
    * Compression is (essentially) LZSS with no Huffman post-coding,
        and some window size tweakage.
    * Contains authoritative offsets for VBA text in streams
    * re-compression a total pain; managed to get Excel to accept
        a re-compressed 'dir' - by truncating a number of the longer
	back-matches to < 1/2 the window size.
    * altering the offsets - works.
    * Stream format is:
	    + 2 byte tag, 4 byte length, <data> [ repeat ]
	    + the tag 0x9 is broken: it's length is 2 bytes too short.
    * Each Stream has 4 strings: ascii/unicode pairs
	    + unicode canonical; 1st pair: unknown, 2nd: stream name.
	    + serious problems if all names not in sync (hmm)


    * Cutting / reduction:
	    + Removing both external linkage records + prepended 2 name
	      pair works fine.
	    + fiddling with the object count - appears to have
	      little effect on OfficeXP - reads to EOF.
	    + removing objects:
		    + removing SHORT_OBJECT_COUNT -> Sheet1's name ->
		      crashes Excel (even with decrementing the count)
		    + If the equivalent PROJECT reference removed -
		      works fine, can remove all Sheets.
		    + can remove workbook if not in PROJECT.
	    + not understood fields:
		+ Fields 0x13, 0x2c - can be 00'd with no apparent problems
	    + Binning all the VBA stream names (ie. not Sheet*,wbk) results
	      in very odd loading - populates project tree just fine, (from
	      OLE stream names?) - but code view / calculate hangs the
	      editor; hmm.

    * finally realised that the _VBA_PROJECT_CUR/PROJECT and PROJECTwm
      streams are rather important.

    * PROJECTwm - looks like an i18n hash; 8bit -> 16bit; simple list,
      all 0 terminated with a trailing 16bits of 0.
	+ what is VersionCompatible32="393222000" ?


* Office 97 quirks:

    + exports a '_VBA_PROJECT' storage - but can just trash it.
	+ this is for backwards compatibility with Office 95
	+ Office 95 doesn't have a _VBA_PROJECT stream.
    + everything very fragile until you delete the __SRP_X
      streams.
    + Clobbering the 'byte 3' _VBA_PROJECT version works nicely,
      [ you can flawlessly export OfficeXP to Office97 macros ].
    + Binning the 'PROJECTwm' stream appears to have no effect though
      Also mangling down the PROJECTwm set to only the macro names
      works fine.
    + Serious problems arise when we omit the 'Sheet 1' type
      references in the PROJECT stream.
	+ we can omit them from the [Workspace] section,
	+ we must have lots of 'Document=' nodes.
	+ [HostExtenderInfo] not necessary.
	+ HelpContextID, HelpFile, Name not necessary.
	+ CMG, DPB, GC: not necessary
	+ VersionCompatible32="393222000" not necessary
	    + Sheet names must be there; Foo1,Foo2,Foo3 no good.
		+ they must exactly match the 'dir' entries [I guess]
		+ The 'dir' entries must be there too ...
	+ Workbook & Sheet streams ...
	    The 'Workbook' stream must contain _at least_:
		+ Attribute VB_Base = "0{00020819-0000-0000-C000-000000000046}"
	    The 'Sheet' stream must contain _at least_:
		+ Attribute VB_Base = "0{00020820-0000-0000-C000-000000000046}"
	+ Naming consistency
	    + 'Workbook' name (stream & PROJECT) _must_ match with
	       Excel 'CODENAME' (0x01ba) record, or SEGV result.
	    + Similarly, Sheet 'CODENAME' records must also match.
		    [ XclCodename record ]
	+ Office 97 also segv's if we don't have a valuid
	    + Attribute VB_Name = "<MacroSheet>"
	    record in the macro ...


** Appendix 1: Random _VBA_PROJECT observations:
   
    + Examining a typical stream;

00000000  cc 61 5e 00 00 01 00 ff  09 08 00 00 09 04 00 00  |Ìa^....ÿ........|
          ^^^^^^^^^^-1-^^^^^^^^^^  ^^^^-2-^^^^ ^^^^-3-^^^^
00000010  e4 04 01 00 00 00 00 00  00 00 00 00 01 00 05 00  |ä...............|
	  ^-4-^ ^-A-^ ^-B-^ ^-C-^  ^-D-^ ^-E-^ ^-F-^ ^-G-^
00000020  02 00 16 01 2a 00 5c 00  47 00 7b 00 30 00 30 00  |....*.\.G.{.0.0.|
          ^-H-^

[1]   - version / magic
[2/3] - language identifiers
[4]   - char-set
Lengths:
[A]   - 
[B]   - 
[C]   - 
[D]   - 
[E]   - 
[F]   - 
[G]   - number of plugins / strings.
[H]   - 

      ... a number of strings ...
      VBA section:

00000770  0b 00 02 00 02 00 02 00  02 00 01 00 01 00 01 00  |................|
	  ^-1-^ ^^^^^^^^^^^^^^^^^^^^^^^^^^^-2-^^^^^^^^^^^^
00000780  01 00 02 04 02 04 02 04  03 00 04 02 00 00 06 02  |................|
          ^^^^^^^^^^^^^^^^^^^^^^^  ^-3-^ ^^^^^^^^^^^ ^-4-^
00000790  01 00 08 02 00 00 0a 02  ff ff ff ff ff ff 00 00  |................|
          ^^^^^^^^^^^^^^^^^ ^^^^^^^^^-5-^^^^^^^^^^^^
-000007a0  00 00 ff ff 00 00 5a f6  67 40 03 00 00 00 01 00  |......Z.g@......|



	This is all tedious overall project stuff so far ...

[1] - count of VBA project elements ...
[2] - element types - each USHORT:
	0x1   == VBA module,
	0x2   == sheet/workbook,
	0x402 == class or form
[3] - count of int32s - tags of some form (?); effectively magic:
[5] - an offset table in 16bit chunks (?)
	+ fixed length of 100bytes
