This is how I managed to hack the visual format language to center a few views vertically (most other ways put them at the top and bottom, or just the top, or just the bottom). Basically what I'm doing is saying that the top margin should be less than or equal to half the portrait height minus the total height of all the views you'll be centring…

vertical_centering_with_vfl.rb

totalCombinedViewHeight = 100

Motion::Layout.new do |layout|
  layout.view view
  layout.subviews "state" => @state, "action" => @action
  layout.metrics "margin" => 20, "height" => 40, "halfHeight" => ((view.bounds.size.height - totalCombinedViewHeight) / 2), "halfWidth" => ((view.bounds.size.width - 100) / 2)
  layout.vertical "|-(<=halfHeight)-[state]-margin-[action]-(>=halfWidth)-|"
  layout.horizontal "|-margin-[state]-margin-|"
  layout.horizontal "|-margin-[action]-margin-|"
end