.bphys file format document?

I’d like to export data (such as velocity at each grid point) out of the .bphys file. I’ve been googling for an “export” function but can’t find it. Failing that, I’ve been googling to find the file format, which I could read with Python. Anyone have a good link for either of these? (I found only a vague reference to it being floating-point numbers.)

Actually - I’d just like to be able to export the physics data - but File -> Export doesn’t seem to support that. Can anyone please help? I’m currently looking through the Python scripts listing, but they don’t seem to do what I need.