title: RegEx word performance: \w vs [a-zA-Z0-9_]
body: <p>I'd like to know the list of chars that <code>\w</code> passes, is it just <a href="https://stackoverflow.com/a/11874899/6553328"><code>[a-zA-Z0-9_]</code></a> or are there more chars that it might cover? </p>
  
  <p>I'm asking this question, because based on <a href="https://stackoverflow.com/a/891741/6553328">this</a>, <code>\d</code> is different with <code>[0-9]</code> and is <a href="https://stackoverflow.com/questions/16621738/d-is-less-efficient-than-0-9">less efficient</a>. </p>
  
  <blockquote>
    <p><code>\w</code> vs <code>[a-zA-Z0-9_]</code>: which one might be faster in large scale? </p>
  </blockquote>