"Does it exist and where can I find it?"

Appendix B of the P6 gives some basic information about the file structure.

There is (or was) a site that listed the meanings of the "GetStringRes" values, but I've not seen an attempt to list the keywords used.

Your best bet would be to mine the executable for strings (Dodger mentioned this once if you can locate the thread).

One attempt at parser is -> ThePoserParser v0.1

Dodger posted some scripts at RFI that might be of use -> http://rfi.elgeneralisimo.com/forums/index.php/topic,57.0.html

There's a decision you have to make when writing a parser for Poser files, which is whether to include all the keywords and their substructure, or leave a more detailed interpretation to something else.
My own attempts at parsing Poser files have concentrated on the latter.
IMHO it's a pity EF didn't introduce an XML based format.