title: Highlight all searched words
body: <p>In my <code>RichtextBox</code>, if I have written as below.</p>
  
  <blockquote>
    <p>This is my pen,<br>
    his pen is beautiful.</p>
  </blockquote>
  
  <p>Now I search word "is" then
  output would be as below.</p>
  
  <p>All "is" should be highlighted.</p>