title: regular expression back referencing
body: <p>why this snippet:</p>
  
  <pre><code>'He said "Hello"' =~ /(\w)\1/
  </code></pre>
  
  <p>matches <code>"ll"</code>? I thought that the <code>\w</code> part matches <code>"H"</code>, and hence <code>\1</code> refers to <code>"H"</code>, thus nothing should be matched? but why this result?</p>