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<?php
/*
 * Customize Menu Item Classes
 *
 * @param array $classes, current menu classes
 * @param object $item, current menu item
 * @param object $args, menu arguments
 * @return array $classes
 */
function wp_nav_parent_class( $classes, $item ) {
    if( is_singular('spaces') && $item->title == "Spaces" ){
        array_push($classes, 'current-menu-item');
    }
	return $classes;
}

add_filter('nav_menu_css_class', 'wp_nav_parent_class', 10, 2);