message: Place XML comments in front of xacro commands
  ... to hide them in the final URDF
diff: <?xml version='1.0' encoding='utf-8'?>
  <robot xmlns:xacro="http://www.ros.org/wiki/xacro" name="panda">
  - <xacro:arg name="arm_id" default="panda" /> <!-- Name of this panda -->
  - <xacro:arg name="hand" default="false" /> <!-- Should a franka_gripper be mounted at the flange?" -->
  - <xacro:arg name="gazebo" default="false" /> <!-- Is the robot being simulated in gazebo?" -->
  + <!-- Name of this panda -->
  + <xacro:arg name="arm_id" default="panda" />
  + <!-- Should a franka_gripper be mounted at the flange?" -->
  + <xacro:arg name="hand" default="false" />
  + <!-- Is the robot being simulated in gazebo?" -->
  + <xacro:arg name="gazebo" default="false" />
  <xacro:unless value="$(arg gazebo)">
  <!-- Create a URDF for a real hardware -->
  