title: git tagging `HEAD` or branches
body: <p>Assume I have a git repository where the current <code>HEAD</code> points to commit <code>abc123</code>, which is the newest commit in <code>myBranch</code>. </p>
  
  <p>When I create a tag, pointing at <code>HEAD</code> (or alternatively <code>myBranch</code>), will that tag point to </p>
  
  <p>a) the commit <code>abc123</code>, which will always be the same?</p>
  
  <p>b) <code>HEAD</code> (or alternatively <code>myBranch</code>), which can vary?</p>