First, I've read perlop, thank you :)

Second, guess, You are wrong, it's not built in function:

use 5.010;
use strict;

sub mysub($)
{
    printf "Sub called with %s\n", join '', @_;
}

sub mysub2
{
    printf "Sub2 called with %s\n", join '', @_;
}

mysub "test" eq "test";
mysub2 "test" eq "test";
[download]

mysub behaves like named unary op (because of proto i belive) and mysub2 behaves like list operator without parens.

Again, I need 100% sure explanation (not guesses) and point where I can find the list of named unary built ins without digging all the perldocs.