'Min' is the time (in minutes) an object without an explicit expiry time should be considered fresh. The recommended value is 0; any higher values may cause dynamic applications to be erroneously cached unless the application designer has taken the appropriate actions.

'Percent' is a percentage of the objects age (time since last modification age) an object without explicit expiry time will be considered fresh.

'Max' is an upper limit on how long objects without an explicit expiry time will be considered fresh.
Options:

override-expire
override-lastmod
reload-into-ims
ignore-reload

override-expire enforces min age even if the server sent a Expires: header. Doing this VIOLATES the HTTP standard. Enabling this feature could make you liable for problems, which it causes.

override-lastmod enforces min age even on objects that was modified recently.

reload-into-ims changes client no-cache or ``reload'' to If-Modified-Since requests. Doing this VIOLATES the HTTP standard. Enabling this feature could make you liable for problems, which it causes.

ignore-reload ignores a client no-cache or ``reload'' header. Doing this VIOLATES the HTTP standard. Enabling this feature could make you liable for problems, which it causes.

Basically a cached object is: (the order is changed from 1.1.X)

FRESH if expires < now, else STALE
STALE if age > max
FRESH if lm-factor < percent, else STALE
FRESH if age < min
else STALE

The refresh_pattern lines are checked in the order listed here. The first entry which matches is used. If none of the entries match, then the default will be used. Click Here to know more about Refresh_Pattern.

Example
For example, setting reference_age to '1 week' will cause objects to be removed if they have not been accessed for a week or more. The default value is one year.
Specify a number here, followed by units of time. For example:

1 week
3.5 days
4 months
2.2 hours

quick_abort_min (KB)
quick_abort_max (KB)
quick_abort_pct (percent)