Add HTML attribute to WordPress menu item

gistfile1.php

<?php // DO NOT COPY THIS TOP LINE

function sd_nav_menu_attr( $atts, $item, $args )
{
	// The ID of the target menu item
	$menu_target = 99;

	// inspect $item
	if ($item->ID == $menu_target) {
		$atts['attribute_name'] = "attribute_value";
	}
	return $atts;
}
add_filter( 'nav_menu_link_attributes', 'sd_nav_menu_attr', 10, 3 );