What is correct selector for radios to determine if ANY radio is selected? Using #states to change form element visibility, I would like a 2nd element to be visible only if the 1st element is filled in. The first element is a pair of radio buttons, so I tried: 

  '#states' =&gt; array('visible' =&gt; array(
  ':input[name="radio-id"]' =&gt; array('value' =&gt; '0', 'value' =&gt; '1'),
    ),),


However that doesn't work, the 2nd value condition clobbers the first, so the other element only appears if the 2nd radio ('1') is checked. So then I tried: 

    :input[name="radio-id"]' =&gt; array('checked' =&gt; TRUE),


Nope, that doesn't work either. 

What is the correct syntax to use for this, and which documentation page is it on? (drupal.org or other site?) I've looked and looked but can't find it.
Had same problem today. A slight modification of the negated value expression proposed on this comment: "Empty Radio Selection" on drupal_process_states() API page, did the trick for me!

'#states' =&gt; array(
   'visible' =&gt; array(
     ':input[name="radios-name"]' =&gt; array('!value' =&gt; false),
   ),
 ),


I just wanted the select list with the above #states entry to be invisible while no selection has still been made on my list of five radios (sharing name "radios-name"). 

Radios were also '#required' => true, in my case and all 5 individual radio-buttons have non-numeric string values. No #default_value is specified in my case either.

Disclaimer: I have only tested this on Chrome!