bp_core_create_subnav_link( array|string $args = '', string $component = 'members' )

function bp_core_create_subnav_link( $args = '', $component = 'members' ) {
	$bp = buddypress();

	$r = wp_parse_args( $args, array(
		'name'              => false, // Display name for the nav item.
		'slug'              => false, // URL slug for the nav item.
		'parent_slug'       => false, // URL slug of the parent nav item.
		'parent_url'        => false, // URL of the parent item.
		'item_css_id'       => false, // The CSS ID to apply to the HTML of the nav item.
		'user_has_access'   => true,  // Can the logged in user see this nav item?
		'no_access_url'     => '',
		'site_admin_only'   => false, // Can only site admins see this nav item?
		'position'          => 90,    // Index of where this nav item should be positioned.
		'screen_function'   => false, // The name of the function to run when clicked.
		'link'              => '',    // The link for the subnav item; optional, not usually required.
		'show_in_admin_bar' => false, // Show the Manage link in the current group's "Edit" Admin Bar menu.
	) );

	// If we don't have the required info we need, don't create this subnav item.
	if ( empty( $r['name'] ) || empty( $r['slug'] ) || empty( $r['parent_slug'] ) || empty( $r['parent_url'] ) || empty( $r['screen_function'] ) )
		return false;

	// Link was not forced, so create one.
	if ( empty( $r['link'] ) ) {
		$r['link'] = trailingslashit( $r['parent_url'] . $r['slug'] );

		$parent_nav = $bp->{$component}->nav->get_primary( array( 'slug' => $r['parent_slug'] ), false );

		// If this sub item is the default for its parent, skip the slug.
		if ( $parent_nav ) {
			$parent_nav_item = reset( $parent_nav );
			if ( ! empty( $parent_nav_item->default_subnav_slug ) && $r['slug'] === $parent_nav_item->default_subnav_slug ) {
				$r['link'] = trailingslashit( $r['parent_url'] );
			}
		}
	}

	// If this is for site admins only and the user is not one, don't create the subnav item.
	if ( ! empty( $r['site_admin_only'] ) && ! bp_current_user_can( 'bp_moderate' ) ) {
		return false;
	}

	if ( empty( $r['item_css_id'] ) ) {
		$r['item_css_id'] = $r['slug'];
	}

	$subnav_item = array(
		'name'              => $r['name'],
		'link'              => $r['link'],
		'slug'              => $r['slug'],
		'parent_slug'       => $r['parent_slug'],
		'css_id'            => $r['item_css_id'],
		'position'          => $r['position'],
		'user_has_access'   => $r['user_has_access'],
		'no_access_url'     => $r['no_access_url'],
		'screen_function'   => &$r['screen_function'],
		'show_in_admin_bar' => (bool) $r['show_in_admin_bar'],
	);

	buddypress()->{$component}->nav->add_nav( $subnav_item );

	return $subnav_item;
}