rezigned

((?=.*\d)(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%]).{7,20})


(           # Start of group
  (?=.*\d)      #   must contains one digit from 0-9
  (?=.*[a-z])       #   must contains one lowercase characters
  (?=.*[A-Z])       #   must contains one uppercase characters
  (?=.*[@#$%])      #   must contains one special symbols in the list "@#$%"
              .     #     match anything with previous condition checking
                {7,20}  #        length at least 7 characters and maximum of 20