What is difference between a node with ns and node inside group with same namespace?

edit

A node in ROS can have ns as an attribute that starts node in given namespace.

A node also be grouped inside a namespace by nesting it under group tag.

But is different in both scenario.

For me both types of code are giving different behavior:

Type 1:

<node name="controller_spawner$(arg robot_name)" pkg="controller_manager" type="spawner" respawn="false"
output="screen" ns="/$(arg robot_name)" args="joint1_velocity_controller joint2_velocity_controller                                  front_left_steering_position_controller front_right_steering_position_controller  joint_state_controller"/>

Type 2:

 <group="$(arg robot_name)">
    <node name="controller_spawner$(arg robot_name)" pkg="controller_manager" type="spawner" respawn="false"
    output="screen" args="joint1_velocity_controller joint2_velocity_controller                                  front_left_steering_position_controller front_right_steering_position_controller  joint_state_controller"/>
</group>

Type 1 runs successfully and I get console output as:

Started controllers: joint1_velocity_controller, joint2_velocity_controller, front_left_steering_position_controller, front_right_steering_position_controller, joint_state_controller

Type 2 fails I get following output in console:

Controller Spawner couldn't find the expected controller_manager ROS interface.