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 turned on (either Smarty::CACHING_LIFETIME_CURRENT or Smarty::CACHING_LIFETIME_SAVED) for
$cache_lifetime to have any purpose.
A $cache_lifetime 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 = Smarty::CACHING_OFF).
If you want to give certain templates their own cache lifetime,
you could
do this by setting
$caching = Smarty::CACHING_LIFETIME_SAVED,
then set $cache_lifetime to a unique value just
before calling display()
or fetch().
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.