Acts as a generic container of options that it passes
down to its children. The `x` and `y` are special in this example,
serving as the pointer's position. Notice that the :rect is
hard-coded at (0,0) but the :div is passing its own position down.
[:div
{:x x, :y y}
[:fill
{:color "lightblue"}
[:rect {:x 0, :y 0, :width 100, :height 100}]]]