$re = '/>(occurence(?:\s(?:[\w\']+),?){0,100})|((?:\s(?:[\w\']+)){0,100}\s?occurence(?:\s(?:[\w\']+),?){0,100})|((?:\s(?:[\w\',]+)){0,100}\s?occurence)</';
$str = '<p>Do not forget the error handling, I don\'t exactly know what happens if it wants to replace an occurence and can\'t find it</p>
<p>Edit: If you have multiple entries which should be replaced, loop the replace part until it will not be able to replace anymore then it will throw an error you can catch to continue</p>';
preg_match($re, $str, $matches, PREG_OFFSET_CAPTURE, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php