The reply set is sorted: the first replies are the most relevant for the query — the last replies being the least relevant. Reply sets can hold several million documents. They are never extensively presented to the user because this would take a lot of time, and consume vast amounts of resource both on the search engine servers, and on the client side.
To avoid this waste of resources leading to huge and unusable results, AFS returns a subset of the reply set, called a reply page, alongside with facets. Facets allows the user to navigate through the results and filter them, while a reply page acts like a window on the reply set, displaying the replies in a given interval (the first ten replies, the replies numbered 41 to 60, and so on).