title: How to use the input/output elements in webflow?
body: <p>I'm trying to understand how the input and output elements are used in webflow. The documentation suggests that flow input/output mapping is similar to calling a method with a signature, but I don't understand what passes the flow the input value or what the flow returns output to. How do I use these elements? </p>
  
  <p>I've been reading the documentation found <a href="https://docs.spring.io/spring-webflow/docs/current/reference/html/defining-flows.html" rel="nofollow noreferrer">here</a>, but there are no examples of the elements in action that I can find. This is an example from the documentation.</p>
  
  <pre><code>&lt;flow xmlns="http://www.springframework.org/schema/webflow"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://www.springframework.org/schema/webflow
                        http://www.springframework.org/schema/webflow/spring-webflow.xsd"&gt;
  
  &lt;input name="hotelId" /&gt;
  
  &lt;on-start&gt;
      &lt;evaluate expression="bookingService.createBooking(hotelId, currentUser.name)"
                result="flowScope.booking" /&gt;
  &lt;/on-start&gt;
  
  &lt;view-state id="enterBookingDetails"&gt;
      &lt;transition on="submit" to="reviewBooking" /&gt;
  &lt;/view-state&gt;
  
  &lt;view-state id="reviewBooking"&gt;
      &lt;transition on="confirm" to="bookingConfirmed" /&gt;
      &lt;transition on="revise" to="enterBookingDetails" /&gt;
      &lt;transition on="cancel" to="bookingCancelled" /&gt;
  &lt;/view-state&gt;
  
  &lt;end-state id="bookingConfirmed" /&gt;
  
  &lt;end-state id="bookingCancelled" /&gt;
  </code></pre>
  
  <p></p>
  
  <p>In this code, where does the value assigned to "hotelId" come from? Does the input come from the URL? If so, does <code>&lt;input/&gt;</code> behavior change in subflows?</p>