"AP" . join "." - I understand what this is doing, but I don't understand from any documentation what the first argument to map is, generally speaking (everything before the first comma)

map this, that will do this to each element of that, with $_ being aliased to each of the elements

For example

my @in  = 1 .. 5;
my @out = map $_ * 2, @in;    # doubles each element of @in
   @out = map $_ * 2, 1 .. 5; # same thing - any list will do
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