update readme

Author: Emmanuel

README.md

@@ -101,9 +101,11 @@ A rule is a boolean test on your configuration and objects.
 
 Rules are defined within a rule set. You can defined as rule sets as you need.
 
-To be selected ("matched"), an object should match ONE or more rule sets. If none of the rule sets are validated by the object, it is considered as "not matched"...
+If all the rules in a rule set are valid ('and'), then the object is selected.
 
-The rules will generally be based on pre-defined test functions as "is property xxx of object equal this value?" (ObjectPropertySet), "is property value is selected in the filtering configuration?" (MatchProperty), ...
+Hence, to be selected ("matched"), an object should match ONE rule set. If none of the rule sets are validated by the object, it is considered as "not matched"...
+
+The rules will be based on pre-defined test functions as "is property xxx of object equal this value?" (ObjectPropertySet), "is property value is selected in the filtering configuration?" (MatchProperty), ...
 
 So, you first define your rule set, then add rules in it, then define a second rule set, and so on...