and the latter a straight loop counter similar in semantics as C's for() loop.

The latter is essentially syntactic sugar for a while loop. Consider:

for (my $n=1;$n<=10;$n++) { ... }
# essentially becomes
{
  my $n=1;
  while ($n<=10) {
    ...
  } continue {
    $n++;
  }
}
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Its my understanding that the continue part of while was specifically introduced to provide the c-style for loop behaviour.