title: Reference filters from different svg file
body: <p>How do you reference filters which are defined in a different file? For instance there is a <code>filter.svg</code> in the folder <code>assets</code> which has:</p>
  
  <pre><code>&lt;svg xmlns="http://www.w3.org/2000/svg"&gt;
    &lt;defs&gt;
      &lt;linearGradient id="gradient"&gt;
        &lt;stop offset="20%" stop-color="#39F" /&gt;
        &lt;stop offset="90%" stop-color="#F3F" /&gt;
      &lt;/linearGradient&gt;
    &lt;/defs&gt;
  &lt;/svg&gt;
  </code></pre>
  
  <p>Now in another file I draw some shapes in another <code>svg</code> element. How do I apply this gradient filter? Simply: <code>fill="url(assets/filter.svg#gradient)"</code>? Because it looks like it is not picking up the definition.</p>