In Select2 3.x, the dropdown is attached to the body element and
it is floated above all other elements.
In Select2 4.x, the dropdown is attached directly to the Select2
container, which allows us to skip any special placing logic. This
happens to be how Chosen currently does it, and it prevents us
from having the dropdown display up, as well as a few other strange
issues that can't be prevented.
This new module will most likely become the default, as it matches
the functionality of Select2 3.x and has quite a few advantages.
The other positioning code will need to be broken out into a
separate module in the future.
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