This is the length of time in seconds that a template cache is valid. Once this time has expired, the cache will be regenerated. $caching must be set to "true" for $cache_lifetime to have any purpose. A value of -1 will force the cache to never expire. A value of 0 will cause the cache to always regenerate (good for testing only, to disable caching a more efficient method is to set $caching = false.)
该变量定义模板缓存有效时间段的长度(单位秒),一旦这个时间失效,则缓存将会重新生成.如果要想实现所有效果,$caching必须因$cache_lifetime需要而设为"true".值为-1时,将强迫缓存永不过期.0值将导致缓存总是重新生成(仅有利于测试,一个更有效的使缓存无效的方法是设置$caching = false.)

If $force_compile is enabled, the cache files will be regenerated every time, effectively disabling caching. You can clear all the cache files with the clear_all_cache() function, or individual cache files (or groups) with the clear_cache() function.
如果启动了强迫编译,则缓存文件每次将会重新生成.要想有效地停止缓存,你可以利用clear_all_cache() 函数清除所有的缓存文件,或者利用clear_cache() 函数清除个别文件(或文件组).

Technical Note: If you want to give certain templates their own cache lifetime, you could do this by setting $caching = 2, then set $cache_lifetime to a unique value just before calling display() or fetch().
技巧:如果你想给某些模板设定它们自己的缓存生存时间,你可以在调用display()或fetch()函数之前,通过设置$caching = 2,然后设置$cache_lifetime为一个唯一值来实现.