How double underscore works in cakePHP?

Question

which means, can i change the result of find() to another model using sth like:

<?php 
  fields = array('sum(vote.score) as Post__score_sum'), 
?>

and return:

array(
  'Post'=> array(
    'score_sum' => 5
  )
);

related: http://stackoverflow.com/questions/1611311/cakephp-pagination-sort-data-out-of-model