I was thinking about the “greedy” modifier, and how one would need to use this to avoid simply matching the entire string in a case like the one you have cited.

Ah, you mean as in "something equals /.*?/"? Then here's a question for you. How many times does "FOO.*?BAR" occur in "zero FOO one FOO two BAR three BAR four"?

Where can I perldoc to read more about such Higher Magick, that I may one day Impress My Friends, too?

Except for say, all will be revealed by reading man perlre. (Oh, and if you replace "(*FAIL)" with "(?!)", you could have done the trick ever since 5.005 - it's not something from this century).

Note also that

    /(FOO.*?BAR)(??{ say $1 })(*FAIL)/;
[download]

and

    /(FOO.*BAR)(??{ say $1 })(*FAIL)/;
[download]

print exactly the same matches, although in a possible different order.