title: mkdocs expandable content loads separate md document
body: <p>Is it possible to have an expanded section of a doc load the contents of another md document? The expandable content could be used in other documents, so instead of getting into version hell, I'd like to create one md doc that I can reference. Right now I have links to the doc with the shared content, but it would be nice to have it load as expandable content instead of loading another page.</p>
  <pre><code>&lt;details&gt;
  &lt;summary&gt;Click to expand!&lt;/summary&gt;
    
  Here it would load the contents of another md document.
  
  &lt;/details&gt;
  </code></pre>