Regex for Validating Password

This regex can be use to validate password

((?=.*\d)(?=.*[a-z])(?=.*[A-Z])(?=.*[\W]).{8,20})

description:

(                   # Start of group
  (?=.*\d)          # must contains one digit from 0-9
  (?=.*[a-z])       # must contains one lowercase characters
  (?=.*[\W])        # must contains at least one special character
  .                 # match anything with previous condition checking
  {8,20}            # length at least 8 characters and maximum of 20 
)                   # End of group