Can you help us understand the end goal you plan to achieve after getting familiar with the file format?
Seriously don't you have any idea of the end-goal ?
Fireworks uses PNG as native file format, which is really good, decorated with meta-data to store plots and layers information, still a good idea...
...but does not provide a clear specification of such metadata, which is really bad as it captures users to a proprietary format.
Remember that people use your software because they found it efficient, not because they're obliged to, for interoperabity issues.