# File lib/rack/mount/vendor/regin/regin/group.rb, line 28
    def to_s(parent = false)
      if lookahead == :postive
        "(?=#{expression.to_s(parent)})#{quantifier}"
      elsif lookahead == :negative
        "(?!#{expression.to_s(parent)})#{quantifier}"
      elsif !expression.options?
        "(#{capture ? '' : '?:'}#{expression.to_s(parent)})#{quantifier}"
      elsif capture == false
        "#{expression.to_s}#{quantifier}"
      else
        "(#{expression.to_s})#{quantifier}"
      end
    end