title: How to git-commit from a branch to a detached HEAD?
body: <p>My <em>ref</em> <code>HEAD</code> points the branch <code>foo</code>, that points to the commit <code>123abc</code>; and I have some staged work.</p>
  
  <p>How to <code>git commit</code> that work, moving the <code>HEAD</code> to the newly created commit, but <strong>without advancing the branch</strong>?</p>
  
  <p>(hence: leaving <code>foo</code> point to <code>123abc</code>)</p>
  
  <p>Is it possible to do it with a single <code>git</code> command?</p>