Parameters for cmd_vel_mux

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I wish to adjust the priority of cmd_vel_mux
For this purpose I've located some .YAML files for understanding the syntax.

• name: "Safe reactive controller"
  topic: "safety_controller"
  timeout: 0.2
  priority: 10
• name: "Keyboard operation"
  topic: "keyboard_teleop"
  timeout: 0.2
  priority: 7

I can't figure out what is the exact meaning of these fields - name/topic/timeout/priority.
Of course "name" is a name... But in which namespace? Where do I set this namespace?
"timeout" is a measure of time, guessing - idle time while dealing with the callback, but what units? (second/milliseconds/minutes)
Priority - which is high, which is low? What is the maximum number of priorities available?
Topic - same as name. I do not know any of these topics, they are not available when listing the current topics (rostopic list), so I guess it is also another namespace (?)