Er you mean what setting does what, or...? The format is ascii, plain text. I think Kurokuma(?) made an explanation once on the innards of Poser files.

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You just can't put the words "Poserites" and "happy" in the same sentence - didn't you know that? LaurieA
  Using Poser since 2002. Currently at Version 11.1 - Win 10.