Avoid using classes from the configured package hierarchy outside of the package hierarchy, except when using one of the configured allowed classes. Example:
package some.package;

import some.other.package.subpackage.subsubpackage.DontUseThisClass;

public class Bar {
   DontUseThisClass boo = new DontUseThisClass();
}

This rule is deprecated, use {rule:squid:ArchitecturalConstraint} instead.