|The stupid question is the question not asked|
Thank you for posting such an informative explanation!
After reading and running your examples, I've noticed two minor discrepancies between the descriptions. These might cause some confusion (especially for anyone who can't easily run the examples).
In your first section on 'Numeric Values' the very next sentence after the program listing says "second and third line of the data" which should include "fourth" also (to match the just preceding __OUTPUT__ block).
Then in your third section on 'Numeric and Regular Expressions' the second sentence says "the lines from $. == 1" which should be 2 like the $left side of the following range operator.
I hope that helps a bit.
PeaceOut - Pip@CPAN.Org