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The PDF version I have from Aug 2010 states: "In one sense, a signature is a collection of parameters. Captures fill the same niche for arguments." This does not provide a definition of a capture; it merely provides an analogy to something else. We need a definition.
In what sense is a capture different from an array reference?
Code sample at start of 4.5.1: Does each capture in this array have to have arguments in the same position?
I also found this part of chapter 4 confusing.
Regarding 1 and 2: we now have a proper explanation; please re-read and tell me if it's less confusing now :-)
I've answered 3. in SHA: c4de7ab