What's the use of "Private DICT Data" in Adobes CFF format

Question

As described in Adobes "Compact Font Format" (CFF) specification ( http://partners.adobe.com/public/developer/en/font/5176.CFF.pdf ), theres a "private" font dictionary in CFF compressed postscript fonts (e.g. OpenType fonts with TrueType outlines).

Can someone explain what this "Private DICT Data" in CFF fonts is good for?

And how you can check a font for "Private DICT Data" - e.g. in FontLab Studio?

---

Update:

It seems as if FontLab Studio displays the Private DICT hinting data as follows:

Answer 1

The Private DICT data is the equivalent of a type 1 font Private dict (there are a couple of extra values, defined in the CFF spec). You can find details of the various entries in the Adobe Type 1 Font Format (Chapter 5), I don't have a URL off the top of my head though.

The Private data is where the font-wide hinting information is stored (ie its good for hinting).

You must have a Private DICT, but it can be empty if all values are defaults. I have no idea what (if anything) Font Lab Studio does with the information.