HTML::Selector

selector.rb

    def has_an_nth_child_match?(statement, values, pseudo)
      # Nth-child including last and of-type.
      res = statement.sub!(/^:nth-(last-)?(child|of-type)\((odd|even|(\d+|\?)|(-?\d*|\?)?n([+\-]\d+|\?)?)\)/) do |match|
        reverse = $1 == "last-"
        of_type = $2 == "of-type"
        @source << ":nth-#{$1}#{$2}("
        case $3
          when "odd"
            pseudo << nth_child(2, 1, of_type, reverse)
            @source << "odd)"
          when "even"
            pseudo << nth_child(2, 2, of_type, reverse)
            @source << "even)"
          when /^(\d+|\?)$/  # b only
            b = ($1 == "?" ? values.shift : $1).to_i
            pseudo << nth_child(0, b, of_type, reverse)
            @source << "#{b})"
          when /^(-?\d*|\?)?n([+\-]\d+|\?)?$/
            a = ($1 == "?" ? values.shift :
                 $1 == "" ? 1 : $1 == "-" ? -1 : $1).to_i
            b = ($2 == "?" ? values.shift : $2).to_i
            pseudo << nth_child(a, b, of_type, reverse)
            @source << (b >= 0 ? "#{a}n+#{b})" : "#{a}n#{b})")
          else
            raise ArgumentError, "Invalid nth-child #{match}"
        end
        "" # Remove
      end
      res
    end