title: Exclude characters from a character class
body: <p>Is there a simple way to match all characters in a class except a certain set of them? For example if in a lanaguage where I can use \w to match the set of all unicode word characters, is there a way to just exclude a character like an underscore "_" from that match?</p>
  
  <p>Only idea that came to mind was to use negative lookahead/behind around each character but that seems more complex than necessary when I effectively just want to match a character against a positive match AND negative match. For example if &amp; was an AND operator I could do this...</p>
  
  <pre><code>^(\w&amp;[^_])+$
  </code></pre>