title: The scope of custom helper
body: <p>I have defined my helper function in Helper:</p>
  
  <pre><code>module CarsHelper
  
    def my_helper
      ...
    end
  
  end
  </code></pre>
  
  <p>But I can neither used it(my_helper) in my <code>CarsController</code> nor in <code>Car</code> model, is it so that the custom helper can only be used in View?</p>