title: highlight the word in the string, if it contains the keyword
body: <p>how write the script, which menchion the whole word, if it contain the keyword? <strong>example:</strong> keyword "fun", string - the bird is funny, result - the bird is * funny*. i do the following</p>
  
  <pre><code>     $str = "my bird is funny";
       $keyword = "fun";
       $str = preg_replace("/($keyword)/i","&lt;b&gt;$1&lt;/b&gt;",$str);
  </code></pre>
  
  <p>but it menshions only keyword.  my bird is <strong>fun</strong>ny</p>