# File lib/nanoc/base/compilation/filter.rb, line 183
    def depend_on(items)
      # Notify
      items.each do |item|
        Nanoc::NotificationCenter.post(:visit_started, item)
        Nanoc::NotificationCenter.post(:visit_ended,   item)
      end

      # Raise unmet dependency error if necessary
      items.each do |item|
        rep = item.reps.find { |r| !r.compiled? }
        raise Nanoc::Errors::UnmetDependency.new(rep) if rep
      end
    end