title: How to do a regex search in a GtkSourceBuffer
body: <p>I am using <code>GtkSourceView</code> with a <code>GtkSourceBuffer</code>.</p>
  
  <p>I need to do a regular expression search on its contents, and I know that <code>GtkSourceBuffer</code> is a subclass of <code>GtkTextBuffer</code>.</p>
  
  <p>I'd like to do something like the Python code below, where <code>search_text</code> is a regular expression. </p>
  
  <pre><code>search_text = 'some regular expression'
  source_buffer = source_view.get_buffer()
  match_start = source_buffer.get_start_iter()
  result = match_start.forward_search(search_text, 0, None)
  if result:
      match_start, match_end = result
      source_buffer.select_range(match_start, match_end)
  </code></pre>
  
  <p>The regex isn't too complex: <code>search_text = '/file_name\S*'</code>. (Basically I want to match all file names in a document that are preceded by a separator character <code>/</code>, start with a common file name, and end with a sequence of non-space characters, including the file extension).</p>
  
  <p>The <a href="https://developer.gnome.org/gtk3/stable/GtkTextIter.html#gtk-text-iter-forward-search" rel="nofollow noreferrer"><code>Gtk.GtkTextIter.forward_search()</code></a> function only seems to accept these three flags, so I do not see a way of specifying that the search string is a regular expression...</p>
  
  <pre><code>Gtk.TextSearchFlags.VISIBLE_ONLY
  Gtk.TextSearchFlags.TEXT_ONLY
  Gtk.TextSearchFlags.CASE_INSENSITIVE
  </code></pre>
  
  <p>How can I achieve a regex search on GtkSourceBuffer or GtkTextBuffer ?</p>