title: Regular expression in Vim to match group capture
body: <p>I want to find the words which <strong>contain</strong> the same string repeated twice.
  (e.g. <code>wookokss</code>(ok/ok), <code>ccsssscc</code>(ss/ss)).
  I think the expression is <code>\(\w*\)\0</code>. </p>
  
  <p>Another try is to find the words which <strong>consist of</strong> the same string repeated twice. My answer is <code>\&lt;\(\w*\)\0\&gt;</code>. (word beginning + grouping(word) + group capture + word ending)</p>
  
  <p>But they don't work. Could anybody help me?</p>