We all know that Drupal provides the FormAPI, in which very powerful form
elements exist (in our case, the tableselect element). This magical element behaves like a table, but has a
checkbox for each line, and associated JS/CSS to handle checking rows. But it
is normally impossible to add additional form elements on each row ( there have
been many workarounds, but all seem hackish) due to the way Drupal handles form
submission. This is how to have a clean (and simple!) way to go around those
restrictions.