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

/** FIRST FIELDSET **/

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

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

/** SECOND FIELDSET **/

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

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

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