Highlight search results with PHP

<?
/**
* Perform a simple text replace
* This should be used when the string does not contain HTML
* (off by default)
*/
define('STR_HIGHLIGHT_SIMPLE', 1);

/**
* Only match whole words in the string
* (off by default)
*/
define('STR_HIGHLIGHT_WHOLEWD', 2);

/**
* Case sensitive matching
* (off by default)
*/
define('STR_HIGHLIGHT_CASESENS', 4);

/**
* Overwrite links if matched
* This should be used when the replacement string is a link
* (off by default)
*/
define('STR_HIGHLIGHT_STRIPLINKS', 8);

/**
* Highlight a string in text without corrupting HTML tags
*
* @author Aidan Lister
* @version 3.1.1
* @link http://aidanlister.com/repos/v/function.str_highlight.php
* @param string $text Haystack - The text to search
* @param array|string $needle Needle - The string to highlight
* @param bool $options Bitwise set of options
* @param array $highlight Replacement string
* @return Text with needle highlighted
*/
function str_highlight($text, $needle, $options = null, $highlight = null)
{
// Default highlighting
if ($highlight === null) {
$highlight = '<span class="highlight">$1</span>';
}

// Select pattern to use
if ($options & STR_HIGHLIGHT_SIMPLE) {
$pattern = '#(%s)#';
$sl_pattern = '#(%s)#';
} else {
$pattern = '#(?!<.*?)(%s)(?![^<>]*?>)#';
$sl_pattern = '#(%s)#';
}

// Case sensitivity
if (!($options & STR_HIGHLIGHT_CASESENS)) {
$pattern .= 'i';
$sl_pattern .= 'i';
}

$needle = (array) $needle;
foreach ($needle as $needle_s) {
$needle_s = preg_quote($needle_s);

// Escape needle with optional whole word check
if ($options & STR_HIGHLIGHT_WHOLEWD) {
$needle_s = 'b' . $needle_s . 'b';
}

// Strip links
if ($options & STR_HIGHLIGHT_STRIPLINKS) {
$sl_regex = sprintf($sl_pattern, $needle_s);
$text = preg_replace($sl_regex, '1', $text);
}

$regex = sprintf($pattern, $needle_s);
$text = preg_replace($regex, $highlight, $text);
}

return $text;
}
?>

echo str_highlight($searched_title, $search_keyword);