title: Rewrite URL across all sites in WordPress Multisite
body: <p>I'm building a plugin for a WordPress Multisite, and each subsite needs an SEO friendly URL for various tabs that actually appear on the same page.</p>
  
  <p>I have already written the system that detects the correct URL and shows the relevant tab using a query string, but I want to do it without a query string... here's what I mean:</p>
  
  <p><strong>Currently</strong>:<br/>
  <a href="http://domain.com/subsite/?tab=contact" rel="nofollow">http://domain.com/subsite/?tab=contact</a><br/>
  Will load the home page of the sub-site, but containing the content of the "Contact" tab. i.e.</p>
  
  <pre><code>if (isset($_REQUEST['tab'])) {
      $tab = $_REQUEST['tab'];
      // Validate $tab here
      get_template_part('tab', $tab);
  }
  </code></pre>
  
  <p><strong>What I Need</strong>:<br/>
  <a href="http://domain.com/subsite/contact" rel="nofollow">http://domain.com/subsite/contact</a><br/>
  To be invisibly rewritten for ALL subsites so that it ends up showing the same content, by rewriting /subsite/whatever to /subsite/?tab=whatever</p>
  
  <p>Any and all help would be greatly appreciated.</p>