The syntax should allow to specify what classes should ONLY access

[codecholeric]

While it is easy to do black listing

noClasses().that().resideInAPackage("..foo..").should().accessClassesThat().resideInAPackage("..bar..")

and to control access TO a component

classes().that().resideInAPackage("..bar..").should().onlyBeAccessed().byAnyPackage("..foo..")

it is rather hard to specify that ..foo.. should only access ..bar... The closest way out of the box would be an awkward double negation

noClasses().that().resideInAPackage("..foo..").should().accessClassesThat().resideOutsideOfPackage("..bar..")

It should be possible to specify

classes().that().resideInAPackage("..foo..").should().onlyAccessClassesThat().resideInAPackage("..bar..")

Likewise this should be supported for callMethod, callConstructor and accessField and flavors.