title: How do I assign a custom element's text contents to a template slot?
body: <p>I'm creating some web components and would like to insert the contained text into a template slot. I'd like to make it slottable as opposed to simply copying their value so the browser can naturally handle changes to the text instead of having to pass it through the component itself. </p>
  
  <p>According to MDN textNodes <em>are</em> slottable, however I can't find any real means of doing this aside from the deprecated  element from v1. (textNodes do not support attributes, so I can't simply assign it a slot that way, and .assignedSlot() is read-only.) Support outside the documentation is pretty minimal, although this is to be expected from such a new technology.</p>
  
  <pre><code>&lt;my-element&gt;some text&lt;/my-element&gt;
  
  &lt;template&gt;
   &lt;h3&gt;&lt;slot name="label"&gt;&lt;/slot&gt;&lt;/h3&gt;
   &lt;p&gt;Derp&lt;/p&gt;
  &lt;/template&gt;
  </code></pre>
  
  <p>Using this as a simplified example, I'd like <code>some text</code> to appear in the <code>label</code> slot, and get updated accordingly when the markup changes.
  Is there a good/integrated way to do this? Will I have to resort to a mutationObserver?</p>