FAPI initial checked state for #type => radio Drupal FAPI reference doesn't have a working example for #type=>radio.  How can I indicate that I want the element to be rendered in a checked state?

$form['my_radio_button'] = array(
  '#type' =&gt; 'radio',
  '#default_value' =&gt; TRUE,
  '#title' =&gt; t('Checked by default.'),
);


I've tried #default_value TRUE, 1, and different combinations of #value, but nothing seems to work.  Thanks!
I may be totally remembering this wrong,  but I'm pretty sure you want to add &quot;checked&quot; as an attribute.
attributes =&gt; array(&quot;checked&quot;)