title: Regular Expression: Double Backslashes in Bracket Expression
body: <p>What do the double backslashes in the following expression match?</p>
  
  <pre><code>/^[\\?]/
  </code></pre>
  
  <p>Is it a filter for <code>\</code> and <code>&amp;</code> (escaped backslash) - or - <code>\\</code> and <code>&amp;</code> (not escaped) - or - <code>\</code> and <code>?</code> (escaped question mark)?</p>