title: What does the "percentage sign" mean in the Vue.js source code
body: <p>I am reading Vue.js's source code(<a href="https://github.com/vuejs/vue/blob/dev/src/shared/util.js#L41" rel="nofollow noreferrer">here</a>) on github and stumbled upon something both I don't know and can't find an answer.</p>
  
  <p>A related part from the source:</p>
  
  <pre><code>export function isObject (obj: mixed): boolean %checks {
    return obj !== null &amp;&amp; typeof obj === 'object'
  }
  </code></pre>
  
  <p>What is the function or meaning of the "%"?</p>