Add TinyMCE WYSIWYG (Rich text area) meta box - WordPress

wp_editor( $content, $editor_id, $settings = array() );

add_action( 'add_meta_boxes', 'post_note_meta_box_add' );
function post_note_meta_box_add()
{	
	// Add new meta box
	add_meta_box( '_post_note', 'Notes', 'render_post_note_meta_box', 'post', 'normal', 'default' );
}

function render_post_note_meta_box()
{
	global $post;
	// Get saved meta data
	$post_note_meta_content = get_post_meta($post->ID, '_post_note', TRUE); 
	if (!$post_note_meta_content) $post_note_meta_content = '';
	wp_nonce_field( 'post_note'.$post->ID, 'post_note_nonce');
	// Render editor meta box
	wp_editor( $post_note_meta_content, 'post_note', array('textarea_rows' => '5'));
}

add_action( 'save_post', 'post_note_meta_box_save' );
function post_note_meta_box_save( $post_id )
{
	// Bail if we're doing an auto save
	if( defined( 'DOING_AUTOSAVE' ) && DOING_AUTOSAVE ) return;
	 
	// if our nonce isn't there, or we can't verify it, bail
	if( !isset( $_POST['post_note_nonce'] ) || !wp_verify_nonce( $_POST['post_note_nonce'], 'post_note'.$post_id ) ) return;
	 
	// if our current user can't edit this post, bail
	if( !current_user_can( 'edit_post' ) ) return;
	
	
	// Make sure our data is set before trying to save it
	if( isset( $_POST['post_note'] ) )
		$result = update_post_meta( $post_id, '_post_note', $_POST['post_note'] );
}