How to format the inner of a Digest

Hi,

Setting up my first Subscriptions installation on a Drupal 7 installation and got to the "Mail Templates" to customize the email conent sent to the users. Most of my users will use the Digest mode of Subscripts so that's the first thing I try to customize. I understand the concept of the loop but I didn't get it, where the inner content of every digest item can be templated? As I understand it is renders using the following line:

[subs:items:index:#0:formatted]

Wich gets the "formatted" representation of the item. But how to customize the this?

Any help would be great - thank!
Marc