bp_core_new_subnav_item( array|string $args, string|null $component = null )

function bp_core_new_subnav_item( $args, $component = null ) {
	// Backward compatibility for plugins using `bp_core_new_subnav_item()` without `$component`
	// to add group subnav items.
	if ( null === $component && bp_is_active( 'groups' ) && bp_is_group() && isset( $args['parent_slug'] ) ) {
		/*
		 * Assume that this item is intended to belong to the current group if:
		 * a) the 'parent_slug' is the same as the slug of the current group, or
		 * b) the 'parent_slug' starts with the slug of the current group, and the members nav doesn't have
		 *    a primary item with that slug.
		 */
		$group_slug = bp_get_current_group_slug();
		if (
			$group_slug === $args['parent_slug'] ||
			( 0 === strpos( $args['parent_slug'], $group_slug ) && ! buddypress()->members->nav->get_primary( array( 'slug' => $args['parent_slug'] ), false ) )
		) {
			$component = 'groups';
		}
	}

	if ( ! $component ) {
		$component = 'members';
	}

	if ( ! bp_is_active( $component ) ) {
		return;
	}

	// First, register the subnav item in the nav.
	$subnav_item = bp_core_create_subnav_link( $args, $component );

	/*
	 * To mimic legacy behavior, if bp_core_create_subnav_link() returns false, we make an
	 * early exit and don't attempt to register the screen function.
	 */
	if ( false === $subnav_item ) {
		return false;
	}

	// Then, hook the screen function for the added subnav item.
	$hooked = bp_core_register_subnav_screen_function( $subnav_item, $component );
	if ( false === $hooked ) {
		return false;
	}
}