This is a snippet taken from
init_bounding_box(block, :hold_position => true) do |_|
# Canvas bbox acts like margin_box in that its parent bounds are unset.
@bounding_box = BoundingBox.new(
self, nil, [0, page.dimensions],
:width => page.dimensions,
:height => page.dimensions
It's basically just throwing away the value. A normal do block would have something like |my_var|