What is /utils/exec and where do I find it's documentation

In response to this question on using a conditional to define a TikZ style it was suggested to use /utils/exec.

It is easy to find uses of this, but I have not been able to locate documentation on it. I have looked in the TeXbook and TeX By Topic, but did not find this.

So, where what exactly is /utils/exec and where can I find documentation on it. Under what conditions should one use this or not use this?

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See Section 55.4.8 Handlers for Key Inspection of the pgfmanual. – Gonzalo Medina May 9 '11 at 23:30
@Gonzalo: Could you make that an answer. – Joseph Wright May 10 '11 at 7:02
It is a PGF/TikZ style so it is of course in the pgfmanual. You wont find such things in the TeXBook or in TeX By Topic, they list only plainTeX macros but not (La)TeX packages. – Martin Scharrer May 10 '11 at 7:28
I didn't realize it was a PGF/TikZ style and hence it wasn't obvious to me where to look. Hopefully this will be of help to someone else. – Peter Grill May 10 '11 at 8:09

It is implemented by PGF/TikZ; see Section 82.4.8 Handlers for Key Inspection of the pgfmanual.