WP highlight search terms in results

highlight_results.php

<?php
// Add '<b>' tags to search terms in results
function namespace_highlight_results($text){
  if ( is_search() && !is_admin() ){
    $sr = get_query_var('s');
    $keys = explode(" ",$sr);
    $keys = array_filter($keys);
    $text = preg_replace('/('.implode('|', $keys) .')/iu', '<b>'.$sr.'</b>', $text);
  }
  return $text;
}
add_filter('the_excerpt', 'namespace_highlight_results');
add_filter('the_title', 'namespace_highlight_results');
?>