Usage example:

<code lang="PHP">
<?php

$text = 'Example text where the keywords would be highlighted.';

echo highlight_search_keywords($text);

?>
</code>


Function:

<code lang="PHP">

<?php

function highlight_search_keywords($text)
{
	@extract(@parse_url($_SERVER['HTTP_REFERER']));
	
	if (preg_match('/((fr|g)oogle|msn|yahoo|alexa)/i', $host) AND preg_match('/[qp]=([^&]+)/i', $query, $keywords))
	{
		$keywords = preg_split('/[\s\+\,]+/', rawurldecode($keywords[1]), -1, PREG_SPLIT_NO_EMPTY);
		
		foreach (array_unique($keywords) AS $keyword)
		{
			$text = preg_replace('/('. preg_quote($keyword) .')/i', '<span style="color: red; font-weight: bold;">$1</span>', $text);
		}
	}
	
	return $text;
}


?>

</code>