class_cache.php is a class for caching arbitrary data about files in a given folder. It is intended to be used to reduce the time taken to serve dynamically generated pages. It works by checking if a cache file with a given key exists and is not older the cache expiration period. If it does not exist or has expired, the data is stored in a cache file. Otherwise, the data is retrieved from the cache file. MD5 sums are used to generate the names of the files on which the cached data is stored.