# File lib/sass/tree/mixin_node.rb, line 38
    def _cssize(extends, parent)
      children.map do |c|
        parent.check_child! c
        c.cssize(extends, parent)
      end.flatten
    rescue Sass::SyntaxError => e
      e.modify_backtrace(:mixin => @name, :filename => filename, :line => line)
      e.add_backtrace(:filename => filename, :line => line)
      raise e
    end