$cache_dir
This is the name of the directory where template caches are stored. By default this is "./cache", meaning that it will look for the cache directory in the same directory as the executing php script. You can also use your own custom cache handler function to control cache files, which will ignore this setting.
Technical Note: This setting must be either a relative or absolute path. include_path is not used for writing files.
Technical Note: It is not recommended to put this directory under the web server document root.
忘却曲線を使ってこの知識を確実に記憶に残す
