I think that it would be useful to point out that the loop variable is aliased to each element of the array in turn. It is not a copy of the element, so modifying the loop variable will modify the original array. One simple application of this is the initialisation of an array.

# Initialise an array so that $array[n] = n
my $n = 0;
foreach (@array) {$_ = $n++}
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