Question

Could any of you pls explain the following code. For eg., Why D,d is used for?

NOT(REGEX(Phone, "\\D*?(\\d\\D*?){10}"))

Answer 1

The double backslashes are used because of Java’s string escaping rules. The pure regex means:

\D*?   # Match any number of non-digit characters (the "?" is useless here)
(      # Match...
 \d    # a single digit
 \D*?  # optionally followed by any number of non-digits (again, useless "?")
){10}  # Repeat the previous group 10 times.

So this regex matches any string that contains exactly ten digits (plus any number of other, non-digit characters).