    # File lib/action_controller/vendor/html-scanner/html/selector.rb, line 520
        def simple_selector(statement, values, can_negate = true)
          tag_name = nil
          attributes = []
          pseudo = []
          negation = []

          # Element name. (Note that in negation, this can come at
          # any order, but for simplicity we allow if only first).
          statement.sub!(/^(\*|[[:alpha:]][\w\-]*)/) do |match|
            match.strip!
            tag_name = match.downcase unless match == "*"
            @source << match
            "" # Remove
          end

          # Get identifier, class, attribute name, pseudo or negation.
          while true
            # Element identifier.
            next if statement.sub!(/^#(\?|[\w\-]+)/) do |match|
              id = $1
              if id == "?"
                id = values.shift
              end
              @source << "##{id}"
              id = Regexp.new("^#{Regexp.escape(id.to_s)}$") unless id.is_a?(Regexp)
              attributes << ["id", id]
              "" # Remove
            end

            # Class name.
            next if statement.sub!(/^\.([\w\-]+)/) do |match|
              class_name = $1
              @source << ".#{class_name}"
              class_name = Regexp.new("(^|\s)#{Regexp.escape(class_name)}($|\s)") unless class_name.is_a?(Regexp)
              attributes << ["class", class_name]
              "" # Remove
            end

            # Attribute value.
            next if statement.sub!(/^\[\s*([[:alpha:]][\w\-:]*)\s*((?:[~|^$*])?=)?\s*('[^']*'|"[^*]"|[^\]]*)\s*\]/) do |match|
              name, equality, value = $1, $2, $3
              if value == "?"
                value = values.shift
              else
                # Handle single and double quotes.
                value.strip!
                if (value[0] == ?" || value[0] == ?') && value[0] == value[-1]
                  value = value[1..-2]
                end
              end
              @source << "[#{name}#{equality}'#{value}']"
              attributes << [name.downcase.strip, attribute_match(equality, value)]
              "" # Remove
            end

            # Root element only.
            next if statement.sub!(/^:root/) do |match|
              pseudo << lambda do |element|
                element.parent.nil? || !element.parent.tag?
              end
              @source << ":root"
              "" # Remove
            end

            # Nth-child including last and of-type.
            next if 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
            # First/last child (of type).
            next if statement.sub!(/^:(first|last)-(child|of-type)/) do |match|
              reverse = $1 == "last"
              of_type = $2 == "of-type"
              pseudo << nth_child(0, 1, of_type, reverse)
              @source << ":#{$1}-#{$2}"
              "" # Remove
            end
            # Only child (of type).
            next if statement.sub!(/^:only-(child|of-type)/) do |match|
              of_type = $1 == "of-type"
              pseudo << only_child(of_type)
              @source << ":only-#{$1}"
              "" # Remove
            end

            # Empty: no child elements or meaningful content (whitespaces
            # are ignored).
            next if statement.sub!(/^:empty/) do |match|
              pseudo << lambda do |element|
                empty = true
                for child in element.children
                  if child.tag? || !child.content.strip.empty?
                    empty = false
                    break
                  end
                end
                empty
              end
              @source << ":empty"
              "" # Remove
            end
            # Content: match the text content of the element, stripping
            # leading and trailing spaces.
            next if statement.sub!(/^:content\(\s*(\?|'[^']*'|"[^"]*"|[^)]*)\s*\)/) do |match|
              content = $1
              if content == "?"
                content = values.shift
              elsif (content[0] == ?" || content[0] == ?') && content[0] == content[-1]
                content = content[1..-2]
              end
              @source << ":content('#{content}')"
              content = Regexp.new("^#{Regexp.escape(content.to_s)}$") unless content.is_a?(Regexp)
              pseudo << lambda do |element|
                text = ""
                for child in element.children
                  unless child.tag?
                    text << child.content
                  end
                end
                text.strip =~ content
              end
              "" # Remove
            end

            # Negation. Create another simple selector to handle it.
            if statement.sub!(/^:not\(\s*/, "")
              raise ArgumentError, "Double negatives are not missing feature" unless can_negate
              @source << ":not("
              negation << simple_selector(statement, values, false)
              raise ArgumentError, "Negation not closed" unless statement.sub!(/^\s*\)/, "")
              @source << ")"
              next
            end

            # No match: moving on.
            break
          end

          # Return hash. The keys are mapped to instance variables.
          {:tag_name=>tag_name, :attributes=>attributes, :pseudo=>pseudo, :negation=>negation}
        end