How to determine which element has called (triggered) the AJAX callback function?

Question

For example:

/** FIRST FIELDSET **/

$form['fieldset_1']['enabled'] = array(
  '#type'        => 'radios',
  '#options'     => array(1 => t('Enable'),
                          0 => t('Desable'),
                          ),
  '#ajax'    => array('callback' => 'my_ajax_callback',
                      'wrapper'  => 'my_wrapper_1',
                     ),
);

$form['fieldset_1']['myChangebleField'] = array(
  '#type'   => 'whatever',
  '#prefix' => '<div id="my_wrapper_1">',
  '#suffix' => '</div>',
);

/** SECOND FIELDSET **/

$form['fieldset_2']['enabled'] = array(
  '#type'        => 'radios',
  '#options'     => array(1 => t('Enable'),
                          0 => t('Desable'),
                          ),
  // Now I am calling the same callback function but assigning a different wrapper
  '#ajax'    => array('callback' => 'my_ajax_callback',
                      'wrapper'  => 'my_wrapper_2',
                     ),
);

$form['fieldset_2']['myChangebleField'] = array(
  '#type'   => 'whatever',
  '#prefix' => '<div id="my_wrapper_2">',
  '#suffix' => '</div>',
);

function my_ajax_callback($form, $form_state) {

/**  
 *  How do I figure out which of the element "enabled" was the caller? 
 *
 *  In that way I could do something like:
 **/
   switch($caller){
     case 'fieldset_1':
       // do stuff...
       break;
     case 'fieldset_2':
       // do stuff...
       break;
     // ...
   }

   return $form[$fieldset]['myChangebleField']
}

As seen in the example above, how do I figure out which of the element "enabled" was the caller?

Having two callback functions is not an option as the form elements will be constructed in a dynamic way and I won't actually use a switch statement in the callback function as shown in the example.

Cheers,

Answer 1

Got it!!! This guy here $form_state['triggering_element'] does the trick.