title: Include only specific file patterns in meld comparison
body: <p>I want to compare directories with Meld, but only specific file patterns.
  E.g., only <code>*.c;*.cc;*.icc;*.h</code> files.</p>
  
  <p>Meld can use File Filters, but I could only use them for <strong>exclusion</strong> filtering specific file patterns. That approach is not useful for me, I guess.</p>
  
  <p>Can an <strong>inclusion</strong> filter be applied?</p>
  
  <p>I tried with the idea of "double negation": Excluding "everything but <code>*.c;*.cc;*.icc;*.h</code>", which in effect would include only those patterns.
  <br>
  I tried using File Filters which worked well for listing "everything but ..." using <code>ls -d -- &lt;my_filter&gt;</code> at the command line (see <a href="https://unix.stackexchange.com/q/397885/137608">this</a>). I assume this is a necessary (but not sufficient) condition for any filter to work in Meld.
  None of these worked:</p>
  
  <ol>
  <li><code>!(*.c|*.h|*.cc)</code></li>
  <li><code>!(*@(.c|.h|.cc))</code></li>
  <li><code>!(*.@(c|h|cc))</code></li>
  </ol>
  
  <p><strong><em>Note</em></strong>: I do not mean to use any type of Text Filter, since I do not care at this point about the contents of files, but only about the file names.</p>
  
  <p><strong><em>Note</em></strong> : I have <code>bash</code> and</p>
  
  <pre><code>$ shopt extglob
  extglob on
  </code></pre>