Eh, no, it's using a prototype to act as Perl buildins.... Remember that by default, subroutine calls gobble up all the arguments (unless there are parens), except subroutines that are prototypes to take zero or one argument. Witness:

#!/usr/bin/perl -w

use strict;

sub all {print "@_\n"};

sub gobble_no_proto  {return};
sub gobble_proto ($) {return};

all "foo", "bar", gobble_no_proto "baz", "quux", "fluff";
all "foo", "bar", gobble_proto    "baz", "quux", "fluff";
__END__
foo bar
foo bar quux fluff
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See the difference?

Abigail