title: Validating UTF-8 names in JavaScript (Node.js) with XRegExp
body: <p>I'm trying to check if a given UTF-8 string consists of letters only.<br>
  I tried the solution I found here: <a href="https://stackoverflow.com/questions/6381752/validating-users-utf-8-name-in-javascript">Validating user&#39;s UTF-8 name in Javascript</a></p>
  
  <p>Given string: <code>Ciesiołkiewicz</code><br>
  is tested with <code>var XRegExp = require('xregexp').XRegExp('^\\p{L}+$');</code></p>
  
  <p>And it's not working because of "ł" letter<br>
  I tried <code>XRegExp('^[\\p{Latin}\\p{Common}]+$');</code><br>
  but it's too much, it accepts polish letters but also characters like "$" etc</p>
  
  <p>How can I validate it against letters only? I don't want to type them into regexp manually.</p>