module Regexp::Lexer

def self.ascend(type, token)
  if type == :group or type == :assertion
    @nesting -= 1 if CLOSING_TOKENS.include?(token)
  end
  if type == :set or type == :subset
    @set_nesting -= 1 if token == :close
  end
  if type == :conditional
    @conditional_nesting -= 1 if token == :close
  end
end