Universal Server Group Membership Syntax

Hello everyone,

I am trying to set the Attribute and Value fields in the Group Settings -> Membership section.
The Universal Server admin guide does not clearly state how the syntax should be. If anyone can shed some light on the syntax that is to be used for example to select:

OU=Users,DC=ACTHolding,DC=com,DC=lb

I have attached a screenshot to further clear which section of the GUI i am refering to.

thanks

Thanks