title: Vue.js - Element UI - Form item label slot
body: <p>I would like to know how to use <code>Form Element Slot</code> with <code>vue.js 2.3</code> and <code>element-ui</code>. <a href="http://element.eleme.io/#/en-US/component/form" rel="noreferrer">Documentaton here</a>. So I can insert  <code>html</code> for the label of my form.</p>
  
  <p>I tried this on <code>jsfiddle</code> <a href="https://jsfiddle.net/yk5zqu3d/" rel="noreferrer">here</a>.</p>
  
  <h3>Problem</h3>
  
  <blockquote>
    <p>Unknown custom element: el-form-item-slot</p>
  </blockquote>
  
  <h3>Question</h3>
  
  <p>What is the proper way to implement that? The documentation is not clear on this topic</p>