launch
    LaunchDescription                        # Final return

    actions
        DeclareLaunchArgument                # Launch parameters
        IncludeLaunchDescription            # Import launch file
        ExecuteProcess                        # Run the specified command
        TimerAction                    

    conditions
        IfCondition

    substitutions
        LaunchConfiguration                    # Import the parameters in the launch file
        PathJoinSubstitution                # Link path
        TextSubstitution                    # Parameter value
        PythonExpression

    launch_description_sources
        PythonLaunchDescriptionSource        # Python launch file

lauch_ros
    actions
        Node                                # Node

    FindPackageShare                        # Find packages