Almost all special variables are very edge case. They can look them up, provided they understand perldoc.

I was concentrating on essential concepts which are misunderstood or ignored, like "flattening".

This is not meant to be a tutorial *, people should rather realize where the gaps in their knowledge are.

You can't explain things to people who don't really listen because they think they know it already.

> regex ... map/grep/sort

my colleagues are capable to write millions of LOC without any regex° or map/grep/sort

This should probably be on a secondary list, I didn't want to risk that they depreciate the fist list. (hope you know what I mean)

> $h = {%h} personally I never seen used this way and I'd stress the standard form to take reference as in \%h

Seems like someone misunderstood flattening.... ;-P

*) though it could link into a tutorial or training.

°) well they sometimes use "cargo cult" regexes, i.e. C&P without understanding.

update

That's very a good idea

• Core modules
  Name some standard modules/pragmas you use and explain what for.

they are confronted with CORE, the concept of module installation and can interact with each other.