title: Import Polymer 2 components in Polymer 3
body: <p>I am developing a web component using Polymer v3, and need to include some custom elements defined in legacy Polymer 2 components in the template HTML of my new component. </p>
  
  <p>Since HTML imports are no longer supported in Polymer 3, what approach should I take to include them? If I was using Polymer 2 I could just add the following in my component's HTML file:</p>
  
  <pre><code>&lt;link rel="import" href="../my-legacy-component.html"&gt;
  </code></pre>
  
  <p>I have tried adding the above link into the template HTML of my component, but it appears that doesn't work. I have also tried various <code>import</code> commands to reference the JS files inside the legacy component directly, but received various inscrutable JS errors so I'm not sure if that is the correct way to go either.</p>
  
  <p>I can't believe there isn't a simple way to do this - would the Polymer team really introduce a new version of the library that is completely incompatible with all the components created using older versions?</p>