title: Reference - What does this regex mean?
body: <h2>What is this?</h2>
  <p>This is a collection of common Q&amp;A. This is also a Community Wiki, so everyone is invited to participate in maintaining it.</p>
  <h2>Why is this?</h2>
  <p><a href="/questions/tagged/regex" class="post-tag" title="show questions tagged &#39;regex&#39;" rel="tag">regex</a> is suffering from <em>give me ze code</em> type of questions and poor answers with no explanation. This reference is meant to provide links to quality Q&amp;A.</p>
  <h2>What's the scope?</h2>
  <p>This reference is meant for the following languages: <a href="/questions/tagged/php" class="post-tag" title="show questions tagged &#39;php&#39;" rel="tag">php</a>, <a href="/questions/tagged/perl" class="post-tag" title="show questions tagged &#39;perl&#39;" rel="tag">perl</a>, <a href="/questions/tagged/javascript" class="post-tag" title="show questions tagged &#39;javascript&#39;" rel="tag">javascript</a>, <a href="/questions/tagged/python" class="post-tag" title="show questions tagged &#39;python&#39;" rel="tag">python</a>, <a href="/questions/tagged/ruby" class="post-tag" title="show questions tagged &#39;ruby&#39;" rel="tag">ruby</a>, <a href="/questions/tagged/java" class="post-tag" title="show questions tagged &#39;java&#39;" rel="tag">java</a>, <a href="/questions/tagged/.net" class="post-tag" title="show questions tagged &#39;.net&#39;" rel="tag">.net</a>.</p>
  <p>This might be too broad, but these languages share the same syntax. For specific features there's the tag of the language behind it, example:</p>
  <ul>
  <li>What are regular expression Balancing Groups? <a href="/questions/tagged/.net" class="post-tag" title="show questions tagged &#39;.net&#39;" rel="tag">.net</a></li>
  </ul>