Add optgroup

The plugin works great. I was wondering if it could be added an improvement to include optgroup tag. It should be directly from the $choices variable:

$choices = array(
‘– Make a Selection –‘ => ”,
value_1 => array( ‘Element 1’, ‘optgroup_1’ ),
value_2 => array( ‘Element 2’, ‘optgroup_1’ ),
value_3 => array( ‘Element 3’, ‘optgroup_1’ ),
value_4 => array( ‘Element 4’, ‘optgroup_2’ ),
value_5 => array( ‘Element 5’, ‘optgroup_2’ ),
value_6 => array( ‘Element 6’, ‘optgroup_3’ ),
value_7 => array( ‘Element 7’, ‘optgroup_3’ ),
);

This could also lead to improve the dropdown adding the possibility of more customisation for each element:

value => array( ‘Label’, ‘optgroup’, ‘class string’, ‘id’, ‘javascript’ ),

Thanks in advance for your great plugin.