title: RichTextBox with text filtering
body: <p>How can I implement in <code>richTextBox</code> something like filter (connected e.g. with <code>combobox</code>) that'll be responsible for showing only lines containing selected word (filters)?</p>
  
  <p>I'm not talking about removing other lines - only "hide".</p>
  
  <p>Is it possible?</p>
  
  <p>Eventually I could use another type control, but if it's not neccessary I'd like to use richTextBox.</p>
  
  <p>I thought now, about storing data in some structure, and make filtering based on this used structure. But don't know if it's efficient solution.</p>