Instead of one rule or rule set per targeting item, which is standard in an unregistered site environment, a multisite environment supports one default rule and zero or more site override rules per targeting item.
Default Rules
Each user segment or content group has one default rule. A targeter has one default rule set group.
The default rule is required; it cannot be deleted. The default rule executes on the current site (where the site visitor is), unless a site override rule specifies that site for its own execution. If one or more site override rules, collectively, specify all the sites, the default rule will never be executed. However, the default rule exists for the standard case, as well as for the exceptional one.
Site Override Rules
Each user segment or content group can have zero or more site override rules; a targeter can have zero or more override rule set groups.
Each site override rule specifies one or more sites on which to execute. This enables you to specify different behavior on different sites.
Site override rules must meet the following requirements:
A site override rule must specify at least one execution site.
Two site override rules for the same targeting item (user segment, content group, or targeter) cannot specify the same execution site.
