def match_keys
      values.each do |v|
        Textoken.expression_err("#{v}: is not permitted.") unless yaml.key?(v)
        add_regexps(yaml[v])
      end
    end
def match_keys
      values.each do |v|
        Textoken.expression_err("#{v}: is not permitted.") unless yaml.key?(v)
        add_regexps(yaml[v])
      end
    end
here we do check for option values user supplied
 option values has to be declared at option_values.yml