The CES team updated to include more advanced Custom Search features in developer guide, such as synonym expansion and integration with Subscribed Links. These features let you trick out your search engine and give your users a richer search experience.
Synonym expansion lets you expand a user's search term (such as "running") to include its variants (such as "jogging" and "sprinting"), so users will not need to search for each variant. Subscribed Links enables you to directly answer your users' questions by promoting a specific result at the top of the results page. You can create your own result text and define sets of queries that would trigger subscribed link results