I am not used to Regular Expression. In your example

^
(?=.*[a-z](?)|) # If a-z is found, push to the N stack
(?=.*[A-Z](?)|) # If A-Z is found, push to the N stack
(?=.*[0-9](?)|) # If 0-9 is found, push to the N stack
(?){2} # Pop the last two captures off the N stack
.{8,} # Match eight or more characters

What does (?=.*[a-z](?)|) do? I cannot understand why (?) is taken after .*[a-z] and why .*[a-z] is used instead of [a-z]. Can you please explain in detail?

Thanks in advanced

(7 + (9 * 10))

you can get:

1) 9 * 10
2) 7 + (9 * 10)

With these balancing groups – its possible to make a Script Parser/validater !!

with the counter, you’ll check for start and ending scope…