This package lets you place contents at an absolute position,
anchored at some specified part of the contents, similar to how
TikZ nodes work, though without using the two-pass strategy of
TikZ. It also avoids messing with the order of beamer overlays,
which is what happens when one uses the textpos package with
the overlay option. The solution used is quite straightforward,
combining coffins (using l3coffins) with the placement
mechanisms of atbegshi.
