title: MongoDB RegEx engine completeness
body: <p>According to Mongo documentation it uses PCRE engine, and PCRE support \b and \w  for unicode characters, but following RegEx does not match with Unicode strings, Is there any solution or alternative syntax for it?</p>
  
  <pre><code>// in Mongo console:
   db.col.find({word:/\b\pL\b/});
  
  // in PHP
  (new Mongo())-&gt;db-&gt;col-&gt;find(['word'=&gt;new MongoRegex('/\b\pL\b/u')]);
  </code></pre>