Even writing a stand alone module, you can get some weirdness... A module I recently wrote is injected into an element at the end of the body with a specific MyModuleName as the id attribute... all of my rules were nested #MyModuleName .foo, unfortunately, even with a reset for MyModuleName div... there were some things I didn't catch, only because something else in the project it was being embedded in had defined .foo, and properties I didn't think to reset.

If you're writing a module, best to prefix each class with some abbreviation. `#MyModuleName .mmn-foo` ... much less likely to clash, still need the `#MyModuleName div` reset, but it's better than dealing with weird integration issues.