My solution is to put everything in objects. I get a lot fewer problems that way. X, Y, and Z may all use each other indiscriminately, but because there are no exports, I get no problems. Best of all worlds ;-)

(I'm not using B as an example because we've run into that problem before - just like using $a and $b as example variables gets some unexpected side effects, B as an example package name can get some (rare) unexpected side effects as well.)