# File lib/cairo/paper.rb, line 61
      def register_unit_resolver(from_units, to_units, &resolver)
        from_units = [from_units] unless from_units.is_a?(Array)
        to_units = [to_units] unless to_units.is_a?(Array)
        from_units.each do |from_unit|
          @@unit_resolvers[from_unit] ||= []
          to_units.each do |unit|
            @@unit_resolvers[from_unit] << [unit, resolver]
          end
        end
      end