Is there a way with the Form API to specify that one or more #options in a 'select' element should be disabled? I would like to insert a separator in my dropdown options that is not a selectable value.
If it's really a separator you're looking to add then it might make more semantic sense to use
<optgroup>s to group your select options.
You can do this with the form API simply by wrapping each group you want in the
<select> in an array, keyed by the title you want for the label:
$form['test'] = array( '#type' => 'select', '#title' => 'test', '#weight' => -10000, '#options' => array( 'Group 1' => array( 1 => 'Group 1 Item 1' ), 'Group 2' => array( 2 => 'Group 2 Item 1', 3 => 'Group 2 Item 2' ) ) );
That will produce a select list like this: