list of letters or pattern: :otrwreh
master_letter_freq:
$VAR1 = {
          'w' => 1,
          'h' => 1,
          't' => 1,
          'o' => 1,
          'r' => 2,
          'e' => 1
        };
list of letters or pattern: ---w
thew
trow
list of letters or pattern: