title: OpenAI Gym: Understanding `action_space` notation (spaces.Box)
body: <p>I want to setup an RL agent on the OpenAI <code>CarRacing-v0</code> environment, but before that I want to understand the action space. In <a href="https://github.com/openai/gym/blob/master/gym/envs/box2d/car_racing.py" rel="noreferrer">the code on github</a> line 119 says:</p>
  
  <pre><code>self.action_space = spaces.Box( np.array([-1,0,0]), np.array([+1,+1,+1]))  # steer, gas, brake
  </code></pre>
  
  <p>How do I read this line? Although my problem is concrete wrt <code>CarRacing-v0</code> I would like to understand the <code>spaces.Box()</code> notation in general</p>