See Rob Weir’s blog entry “The Formats of Excel 2007.” Here’s an idea of how things are already reverting to the same old behavior, right when Microsoft is trying to convince the ISO how wonderful for interoperability their spec is supposed to be. Here’s a sample of what Rob says:
The “Excel Macro-Enabled Workbook” option saves as an “xlsxm” extension. It is OOXML plus proprietary Microsoft extensions. These extensions, in the form of binary blob called vbaProject.bin, represent the source code of the macros. This part of the format is not described in the OOXML specification.
This has some interesting consequences. It is effectively a container for source code that not only requires Office to run it, but requires Office to even read it. So you could have your intellectual property in the form of extensive macros that you have written, and if Microsoft one day decides that your copy of Office is not “genuine” you could effectively be locked out of your own source code.
For fun, they also threw in a brand new binary format (why, if the XML version is so great?):
The “Excel Binary Workbook” option caught me by surprise. This is not the legacy binary formats. This is not the new OOXML. This is a new binary format, with an “xlsb” extension. Similar to OOXML it has a Zip container file (the so-called Open Packaging Conventions container file format), but the payload consists (aside from a manifest) entirely binary files.
Stunning. Mind numbing.