How to use ListboxField (multiple selection)

Banner.php

<?php

/**
 * For cool guy @BenENewton
 */
class Banner extends DataObject {
	private static $db = array(
		'Title' => 'Varchar'
	);
	
	private static $has_one = array(
		'Parent' => 'Page'
	);
}

Page.php

<?php

/**
 * Page with a listbox allowing selection of banners
 */
class Page extends SiteTree {
	
	private static $has_many = array(
		'Items' => 'Banner'
	);
	
	public function getCMSFields() {
		$fields = parent::getCMSFields();
		
		// Make default records (quick hack to get them into the db)
		$count = Banner::get()->count();
		if($count == 0) {
			Banner::create(array('Title' => 'First'))->write();
			Banner::create(array('Title' => 'Second'))->write();
			Banner::create(array('Title' => 'Third'))->write();
		}
		
		$fields->addFieldToTab('Root.List', new ListboxField(
			'Items', // Name of has_many (or many_many) relation
			'Items', // Title
			Banner::get()->map('ID', 'Title')->toArray(), // Get source objects
			$this->Items()->column('ID'), // Get ids of currectly selected objects
			null,
			true	// Means make this a multi-select field.
		));
		
		return $fields;
	}
}

class Page_Controller extends ContentController {
	
	
}

Hey I'll look to work this into docs somehow... where do you think would be appropriate?