Please explain the difference between time_to_live and max_idle_time

[contentfree]

Those seem like the same thing. If an entry was added that has a TTL of 60 seconds, then the max it could idle would be 60 seconds. There's obviously two different configurations, so what are the differences between and what are the recommendations for settings relative to each other (e.g. idle time should always be lower that TTL or vice versa)?

(Good candidate for a FAQ or maybe clearer documentation?)