# File lib/sass/util.rb, line 101
    def map_hash(hash)
      # Copy and modify is more performant than mapping to an array and using
      # to_hash on the result.
      rv = hash.class.new
      hash.each do |k, v|
        new_key, new_value = yield(k, v)
        new_key = hash.denormalize(new_key) if hash.is_a?(NormalizedMap) && new_key == k
        rv[new_key] = new_value
      end
      rv
    end