What is the git clone --filter option's syntax? : <p>The Git 2.17 <a href="https://github.com/git/git/blob/master/Documentation/RelNotes/2.17.0.txt" rel="noreferrer">changelog</a> describes this option:</p>

<blockquote>
  <ul>
  <li>The machinery to clone &amp; fetch, which in turn involves packing and 
  unpacking objects, has been told how to omit certain objects using<br>
  the filtering mechanism introduced by another topic.  It now knows<br>
  to mark the resulting pack as a promisor pack to tolerate missing<br>
  objects, laying foundation for "narrow" clones.</li>
  </ul>
</blockquote>

<p>Is this flag ready to be used, or is it most likely quite unstable? Does anyone know the right syntax to pass? Whatever flags I pass are rejected as being an invalid filter-spec. For example, these were my attempts to filter by directory:</p>

<pre><code>git clone file://path --depth=1 --filter '--subdirectory-filter Assets' TestRepo
git clone file://path --depth=1 --filter --subdirectory-filter Assets TestRepo
git clone file://path --depth=1 --filter Assets TestRepo
</code></pre>
