# File lib/haml/buffer.rb, line 234
    def self.merge_attrs(to, from)
      from['id'] = Compiler.filter_and_join(from['id'], '_') if from['id']
      if to['id'] && from['id']
        to['id'] << '_' << from.delete('id').to_s
      elsif to['id'] || from['id']
        from['id'] ||= to['id']
      end

      from['class'] = Compiler.filter_and_join(from['class'], ' ') if from['class']
      if to['class'] && from['class']
        # Make sure we don't duplicate class names
        from['class'] = (from['class'].to_s.split(' ') | to['class'].split(' ')).sort.join(' ')
      elsif to['class'] || from['class']
        from['class'] ||= to['class']
      end

      from_data = from.delete('data') || {}
      to_data = to.delete('data') || {}

      # forces to_data & from_data into a hash
      from_data = { nil => from_data } unless from_data.is_a?(Hash)
      to_data = { nil => to_data } unless to_data.is_a?(Hash)

      merged_data = to_data.merge(from_data)

      to['data'] = merged_data unless merged_data.empty?
      to.merge!(from)
    end