acache config

[Mipam]

Hi All,

I am trying to read more on the acache section in 9.4.0.
However, it's hard to read about this, because there is so little material
available. Currently i only know the acache-enable option, but i didn't see
it in the named.conf.5 manual. The only variable in the named.conf.5
concerning acache is max-acache-size. So where to enable the acache 
with the acache-enable option, also in named.conf or?
Secondly, in the current bind version already a lot of info is cached.
What additional info is cached with the acache section?
I guess the performance gain by this is mainily on bind servers hosting
a lot of domain names?
Bye,

Mipam.