This chapter shows how to cluster different form elements into fieldsets as well as how to expand the Forms API renderable array a tree that preserves the structure and hierarchy of the form. We'll expand the Form Fun example module and talk about the #tree property. This video uses krumo() and dsm() functions. You will need to download, install, and enable the devel module to use these functions. These functions allow you to see what variables are available to you. To accomplish the same task without using the devel module, you can add the following snippet to your module:
drupal_set_message('' . print_r($vars, true) .'');
Note: There is a typo in the code used in this video. The function
form_fun_tree() is missing a parameter, and should be as follows
function form_fun_tree($form, &$form_state).