zend form custom attribute in select option?

I want know how to add custom attribute for option in a select field of Zend form.

PHP:

$option_values = array("multiOptions" => array(
    "US" => "United States",
    "CA" => "Canada",
));

$type=array('big','small');
$option= new Zend_Form_Element_Select('option',  $option_values);

HTML:

<select>
    <option value='US' type='big'>United States</option>
    <option value='CA' type='small'>Canada</option>
</select>

How to add this type attribute in the option?

It is not possible using ZF's implementation of Zend_Form_Element_Select. You need to create your own element. I have done something similar, here's the relevant code:

<?php
require_once 'Zend/Form/Element/Select.php';

/**
 * Select, but with the possibility to add attributes to <option>s
 * @author Dominik Marczuk
 */
class Zend_Form_Element_SelectAttribs extends Zend_Form_Element {

    public $options = array();

    public $helper = 'selectAttribs';

    /**
     * Adds a new <option>
     * @param string $value value (key) used internally
     * @param string $label label that is shown to the user
     * @param array $attribs additional attributes
     */
    public function addOption ($value,$label = '',$attribs = array()) {
        $value = (string) $value;
        if (!empty($label)) $label = (string) $label;
        else $label = $value;
        $this->options[$value] = array(
            'value' => $value,
            'label' => $label
        ) + $attribs;
        return $this;
    }
}

Put this into /library/Zend/Form/Element/SelectAttribs.php. You also need a helper to render the element. Put it into your view helpers directory, name it SelectAttribs.php as well. Here's the contents of my file:

<?php
require_once 'Zend/View/Helper/FormElement.php';

class Zend_View_Helper_SelectAttribs extends Zend_View_Helper_FormElement {
    public function selectAttribs($name, $value = null, $attribs = null, $options = null, $listsep = "<br />\n") {
        $info = $this->_getInfo($name, $value, $attribs, $options, $listsep);
        extract($info); // name, id, value, attribs, options, listsep, disable

        // force $value to array so we can compare multiple values to multiple
        // options; also ensure it's a string for comparison purposes.
        $value = array_map('strval', (array) $value);

        // now start building the XHTML.
        $disabled = '';
        if (true === $disable) {
            $disabled = ' disabled="disabled"';
        }

        // Build the surrounding select element first.
        $xhtml = '<select'
                . ' name="' . $this->view->escape($name) . '"'
                . ' id="' . $this->view->escape($id) . '"'
                . $disabled
                . $this->_htmlAttribs($attribs)
                . ">\n  ";

        // build the list of options
        $list = array();
        $translator = $this->getTranslator();
        foreach ($options as $opt_value => $option) {
            $opt_disable = '';
            if (is_array($disable) && in_array($opt_value, $disable)) {
                $opt_disable = ' disabled="disabled"';
            }
            $list[] = $this->_build($option, $disabled);
        }

        // add the options to the xhtml and close the select
        $xhtml .= implode("\n   ", $list) . "\n</select>";

        return $xhtml;
    }

    protected function _build($option, $disabled) {
        $html = '<option';
        foreach ($option as $attrib => $value) {
            $html .= " $attrib=\"$value\"";
        }
        return $html.$disabled.">".$option['label']."</option>";
    }
}

With this, you should be ready to go:

$elt = new Zend_Form_Element_SelectAttribs('whatever');
$elt->addOption($value,$label,array('attribname' => 'attribvalue'));