> Is it recommended to include the parent class when reopening a child
> class?

If you change the parent class (for whatever reason that might be),
you'll also have to change all locations where the child class is
opened.

IIRC it was once discussed that adding the child class makes added
methods be stacked instead of overwritten. I hope this won't be
included in future versions of ruby due to its cryptic style but there
is a possibility these two versions will behave differently some day
in the future.