The algorithm operates on a special index of expert documents . These are pages that are about a specific topic and have links to many non-affiliated pages on that topic. Pages are defined as non-affiliated if they are authored by people from non-affiliated organizations. Results are ranked based on the match between the query and relevant descriptive text for hyperlinks on expert pages pointing to a given result page. Websites which have backlinks from many of the best expert pages are authorities and are ranked well.